Method and System for Classifying Communication Signals in a Dynamic Spectrum Access System

ABSTRACT

Methods and systems for dynamic spectrum access (DSA) in a wireless network are provided. A DSA-enabled device may sense spectrum use in a region and, based on the detected spectrum use, select one or more communication channels for use. The devices also may detect one or more other DSA-enabled devices with which they can form DSA networks. A DSA network may monitor spectrum use by cooperative and non-cooperative devices, to dynamically select one or more channels to use for communication while avoiding or reducing interference with other devices.

RELATED APPLICATIONS

This application claims priority to U.S. Application No. 61/090,076,filed Aug. 19, 2008, the disclosure of which is incorporated byreference in its entirety for all purposes; this application also is acontinuation-in-part of the following applications: U.S. applicationSer. No. 11/582,496, filed Oct. 18, 2006; U.S. application Ser. No.11/783,563, filed Apr. 10, 2007, which claims priority to U.S.Provisional Application No. 60/877,656, filed Dec. 29, 2006; U.S.application Ser. No. 11/839,496, filed Aug. 15, 2007; U.S. applicationSer. No. 11/839,503, filed Aug. 15, 2007; and U.S. application Ser. No.12/487,257, filed Jun. 18, 2009, which is a continuation of U.S.application Ser. No. 11/432,536, filed May 12, 2006, now U.S. Pat. No.7,564,816, the disclosure of each of which is incorporated by referencein its entirety for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

This invention was made with Government support under contractsFA8750-05-C-0150, FA8750-07-C-0168, FA8750-07-0005, and FA8750-07-C-0169awarded by the Air Force. The Government has certain rights in thisinvention.

BACKGROUND OF THE INVENTION

Cellular phones, personal digital assistants, walkie-talkies, garagedoor openers, computers, wireless routers and other communicationdevices all incorporate radio technology to establish and maintaincommunications over the electromagnetic frequency spectrum. Some radiofrequency (RF) devices, such as cordless telephones, may automaticallysearch for a channel from among those channels assigned for use by thedevice to establish communications and then release the channel when theradio is finished. However, such devices are unable to automaticallyadapt to significant or challenging changes within the network orspectrum environment such as those discussed below.

Networked radios and other devices designed to operate within oneparticular channel or set of channels cannot operate outside of thedesignated channels without appropriate authorization from regulatoryauthorities or spectrum owners and/or modification of the radios. Forexample, a radio may search a specified band to find an open channel forcommunications with the network. The radio will sequentially or randomlystep or hop through the band until an open channel is found or anindication is given (e.g., through a control signal) that the network isotherwise busy (e.g., no channels are available). Such a radio, however,does not determine a new band or frequency range from which to searchfor channels if a channel is not found. Rather, the radio either workswithin its prescribed frequency band according to its fixedcharacteristics (such as transmit power, bandwidth, and modulationscheme), or it does not work at all.

If a typical radio confronts interference, then its communicationssignals may not be transmitted or received. The radio also might receivea command from a base station to shut down for any number of reasons. Asa specific example, under U.S. government regulations, radios operatingon certain frequencies in the 5 GHz band must cease transmissions onthat channel within a specified time from the detection of radarsignals, which have priority over radio transmissions. A typical radiocommunication system, however, is not able to adjust its own operation,and typically cannot independently determine how to overcomeinterference problems such as harmful interference that may endanger thefunctioning of the system, or degrade, obstruct, or repeatedly interruptservice.

Some radios, known as software-defined radios, can be reconfigured usinguser-defined parameters and software-based mechanisms. These radios,however, are not able to dynamically adjust their operating behavioroutside of a predetermined, fixed set of parameters without uploadingnew software to the radio or modifying its hardware.

BRIEF SUMMARY OF THE INVENTION

In an aspect of the invention, a dynamic spectrum access-enabled(DSA-enabled) device may include a detector configured to detect use ofa first region of spectrum during a first time period during which thedevice and a cooperative device refrain from transmitting, a firstcircuit configured to receive data from the detector and to determine atype of signal present in the first region of spectrum, a second circuitconfigured to identify at least one channel suitable for use by thedevice to communicate with the cooperative device based on datagenerated by the detector and the first circuit, a third circuit toinitiate and maintain communication with the cooperative device, and atransceiver to communicate with the cooperative device on the at leastone channel according to instructions received from the third circuit,said transceiver not transmitting during the first time period. Thedynamic spectrum access-enabled device may include various components.For example, the first, second, and third circuits may include a signalclassifier, channel manager, and/or communication coordinator,respectively. Other components may be included, such as a scheduler todirect scanning by the detector. The detector may be configured todetect a transmission sent by the cooperative device during a secondtime period that does not coincide with the first time period, and mayinclude various detectors such as a narrow-band detector, wide-banddetector, TV detector, radar detector, a wireless microphone detector,or any combination thereof. Other cooperative devices also may refrainfrom transmitting during the first time period. The DSA-enabled devicemay include a policy module to store and enforce a spectrum use policy,which may specify a spectrum range not available for use by the device,that is different than the channel identified by the second circuit.Multiple spectrum use policies may be stored, each of which may defineaccess rules for a different spectrum range. The DSA-enabled device mayperiodically receive spectrum use information from the policy modulebased on the spectrum use policies, at a frequency that may be definedby each of the policies. The DSA-enabled device may be capable ofdetecting use of the first region of spectrum after initiatingcommunication with a cooperative device, without causing an interruptionin communication with the cooperative device. The first region ofspectrum may overlap partially or entirely with the channel identifiedby the second circuit. The device may detect use of the first region ofspectrum while concurrently communicating with the cooperative device.The DSA-enabled device may store one or more channel use tables thatlist channels in the first region of spectrum in various categories,such as backup, active, and other categories. The different categoriesof channels may be scanned by the detector at different rates. TheDSA-enabled device may include an antenna, which may be used by thedetector to detect spectrum use, by the transceiver to communicate withthe cooperative device, or a combination thereof. The DSA-enabled devicemay be a secondary device relative to a primary network in the firstregion of spectrum. The DSA-enabled device also may be a base station,and the cooperative device a subscriber unit or other communicationdevice.

An aspect of the invention may include an environmental sensing moduleto detect spectrum availability on a first channel, a module tocoordinate dynamic spectrum access by the device and at least one othercooperative device based on the spectrum availability detected by saidenvironmental sensing module, and a transceiver to communicate with theat least one other cooperative device on a second channel different fromthe first channel and identified as available for use by the devicebased on the spectrum availability detected by the environmental sensingmodule, where the environmental sensing module may be configured todetect spectrum availability on the first channel concurrently with saidtransceiver communicating with the at least one other cooperative deviceon the second channel. The first and second channels may be, forexample, active and backup channels, respectively. The environmentalsensing module may detect spectrum availability of the first channel ata first rate, and of the second channel at a second rate different fromthe first rate. It also may detect spectrum availability on the firstchannel during a first time period during which the device and the atleast one other cooperative device refrain from transmitting. Theenvironmental sensing module may include a first detector to detectwithin a first region of spectrum that includes the first channel and asecond detector to detect within a second region of spectrum, which mayoverlap some, all, or none of the first region. The environmentalsensing module also may detect spectrum availability on the secondchannel concurrently with the transceiver communicating with the atcooperative device on the second channel. The device also may include asignal classifier to classify a signal in the first channel as beingsent by a cooperative device or a non-cooperative device.

In an aspect of the invention, a dynamic spectrum access-enabled devicemay include a first circuit to receive spectrum use data for a region ofspectrum from at least one cooperative device, a second circuit toidentify at least one channel in the region of spectrum suitable for useby the device to communicate with the at cooperative device based ondata received from the cooperative device, a third circuit to initiateand maintain communication with the cooperative device, and a fourthcircuit configured to schedule a time period during which each of thedevice and the cooperative device refrain from transmitting. Thespectrum use data may be collected by the cooperative device during thetime period during which the devices refrain from transmitting. Thedevice may include a policy module to store and enforce a spectrum usepolicy that specifies a spectrum range not available for use by thedevice, which may be different than the channel identified by saidsecond circuit. The device may include a detector to detectnon-cooperative spectrum use in the first region of spectrum. The devicemay operate as a base station in an infrastructure-type network, and mayinclude a fifth circuit to communicate with other base stations in thenetwork. The device may be a primary device for the first region ofspectrum.

In an aspect of the invention, a method of operating a dynamic spectrumaccess-enabled device may include determining a first channelization ofa first region of spectrum, classifying each of a plurality of channelsdefined by the first channelization according to whether the channel isavailable for use by the device, verifying that each of the plurality ofchannels classified as available for use by the device is not prohibitedby a spectrum use policy, communicating with a cooperative device on afirst of the plurality of channels identified as available for use bythe device, monitoring a second region of spectrum for non-cooperativeuse, upon detecting non-cooperative use of the second region ofspectrum, re-classifying at least one of the plurality of channels as nolonger available for use by the device, and upon determining that thedetected non-cooperative use is in a region of spectrum identified bythe device as being likely to experience interference from thecommunication with the cooperative device, ceasing communication on thefirst channel, and establishing communication with the cooperativedynamic spectrum access-enabled device on a second of the plurality ofchannels identified as available for use, where the second of theplurality of channels has not been re-classified as no longer availablefor use by the device. The steps of monitoring and communicating may beperformed concurrently. The second region of spectrum may partially orentirely overlap the first region of spectrum. The spectrum use policymay set various requirements on channel detection and classification,such as a requirement that a channel is classified as available for usea minimum number of consecutive times prior to it being verified asavailable for use, requiring that a channel is classified as availablefor use during a minimum period of time prior to it being verified foruse, or other requirements. The region of spectrum identified by thedevice as being likely to experience interference from the communicationwith the cooperative device may include a channel that is a harmonic ofthe first channel, a cross-product of the first channel and a channel inwhich the non-cooperative use occurs, a predefined offset from the firstchannel, or a combination thereof. The step of monitoring may includedetecting use of the first region of spectrum using a plurality ofdetectors, each of which may be configured to sense transmissions withina portion of the first region of spectrum corresponding to the detector.The step of monitoring also may include defining a second channelizationof the first region of spectrum different from the first channelization,and detecting use of the first region of spectrum based on the secondchannelization. The method may include applying a spectrum use policy toat least one channel not identified as available for use by the device,periodically verifying that each of the channels is available for use bythe device based on the spectrum use policy, or a combination thereof.Each of the plurality of channels may assigned to at least one of aplurality of classifications, and the rate at which each channel isverified as available for use may be determined by the classification towhich the channel is assigned. The classifications may include active,backup, candidate, or possible, where an active channel is a channel inuse by the device, a backup channel is a channel available for use bythe device, a candidate channel is a channel available for use by thedevice and the device has detected a cooperative signal on the channel,and a possible channel is a channel accessible by the device and nototherwise classified. Each channel classified as active may be verifiedas available for use more frequently than each channel classified asbackup, candidate, or possible. The step of monitoring may be performedwithout interrupting communication with a cooperative device. Thenon-cooperative use may be by a device that is a primary device relativeto the cooperative device. The method may include scheduling a firsttime period during which the device and the cooperative device refrainfrom transmitting. During a second time period not coinciding with thefirst, the cooperative device may sense at least one channel to detectspectrum use by a second cooperative device.

According to an aspect of the invention, a method of operating a dynamicspectrum access-enabled device may include communicating among aplurality of cooperative devices on a first channel, determining achannelization that defines a plurality of channels in the first regionof spectrum, assigning each of the plurality of channels in the firstregion of spectrum to at least one of a plurality of classifications,concurrently with said communicating, monitoring the first region ofspectrum for use by a non-cooperative node by sensing the first regionof spectrum with a detector at a first rate, verifying whether each ofthe plurality of channels is available for use at a rate determined bythe classification to which the channel is assigned, and if anon-cooperative signal is detected on the first channel, ceasingcommunication among the cooperative nodes on the first channel andcommunicating among the plurality of nodes on a channel selected fromthe plurality of channels in the first region of spectrum, the selectedchannel being different from the first channel. The first rate may beselected to prevent interference with the non-cooperative node and tomaintain uninterrupted communication among the plurality of cooperativenodes. The channelization of the first region of spectrum may bedifferent from a channelization used to communicate among the pluralityof cooperative nodes on the first channel. The method may includeapplying a spectrum use policy to at least one channel not identified asavailable for use by the device. The rate at which each of the pluralityof channels in the first region of spectrum is verified as available foruse by the device may be based on the spectrum use policy. Each of theplurality of channels may be classified as active or candidate, whereinan active channel is a channel being used by the device, and a candidatechannel is a channel on which the device has detected a cooperativesignal on the channel. Each channel classified as active may be verifiedas available for use more frequently than each channel classified ascandidate. Each of the plurality of channels may be classified asactive, backup, candidate, or possible, where an active channel is achannel being used by the device, a backup channel is a channelavailable for use by the device, a candidate channel is a channel onwhich the device has detected a cooperative signal on the channel, and apossible channel is a channel that is accessible by the device. Eachchannel classified as active is verified as available for use morefrequently than each channel classified as backup, candidate, orpossible.

According to an aspect of the invention, a method of coordinatingcommunication among a plurality of devices may include scheduling afirst time period during which the plurality of devices refrain fromtransmitting that is synchronized among the plurality of devices, andduring a second time period that does not coincide with the first timeperiod, sensing at least one channel to detect spectrum use by at leastone cooperative device on the at least one channel. Each of theplurality of devices may be a dynamic spectrum access-enabled device,and may be capable of communicating on a plurality of channels afterinitialization of communication among the plurality of devices. Thedevices may not be primary devices with respect to the plurality ofchannels. The method also may include scheduling a first plurality oftime periods at regularly-spaced time intervals during which theplurality of devices refrain from transmitting, and repeating thesensing step during each of a second plurality of time periods that donot coincide with any of the first plurality of time periods. The firsttime period may occur at different points in adjacent communicationframes. The second time periods may be scheduled to have random timeintervals between adjacent periods. During the first time period, atleast one of the plurality of devices may use a detector to detectnon-cooperative spectrum use. The first time period may be synchronizedamong substantially all dynamic spectrum access-enabled devices in ageographic region, among all devices in a plurality of dynamic spectrumaccess networks, or a combination thereof. The networks may benon-cooperative or cooperative each other. The step of sensing mayinclude sensing at least one channel to detect cooperative spectrum useat a time selected by the device that does not coincide with the firsttime period. The first time period may be synchronized among a pluralityof non-cooperative dynamic spectrum-enabled networks, for example duringthe synchronizing step. The plurality of devices may include devicesfrom a plurality of non-cooperative dynamic spectrum-enabled networks.

A system according to an aspect of the invention may include a pluralityof dynamic spectrum access-enabled devices, each of which may refrainfrom transmitting during a first time period synchronized among theplurality of devices, and at least one of the devices may include asensor module to detect spectrum use by a device not in the plurality ofdevices during the first time period, and to detect spectrum use by acooperative device during a second time period that does not coincidewith the first time period. Each of the plurality of devices may be adynamic spectrum access-enabled device, and the device not in theplurality of communication devices may be non-cooperative with saidplurality of communication devices. The sensor module may includemultiple sensors. The system may include a circuit such as a schedulerto schedule time periods at regularly-spaced time intervals, duringwhich the plurality of devices refrain from transmitting. The circuitmay be integral to or separate from the devices. At least one of thedevices may include a detector to repeat sensing during each of a secondplurality of time periods, each of which does not coincide with any ofthe first time periods. The second time periods may be scheduled withrandom time intervals between adjacent periods. The detector may beactuated to detect non-cooperative spectrum use. The first time periodmay be synchronized among substantially all the dynamic spectrumaccess-enabled devices in a geographic region, and may occur atdifferent points in adjacent communication frames. Each of the pluralityof devices may sense a channel to detect cooperative spectrum use at atime selected by the device, which may not coincide with the first timeperiod. The devices may include devices from one or more non-cooperativedynamic spectrum-enabled networks, and each of the devices may nottransmit any data other than control data to devices in any of the othernon-cooperative networks.

According to an aspect of the invention, a dynamic spectrum access(DSA)-enabled device may include a first circuit that causes the deviceto refrain from transmitting during a first time period, which may besynchronized among a plurality of other DSA-enabled devices, and asecond circuit to sense at least one channel to detect spectrum use byat least one cooperative DSA-enabled device on the at least one channelduring a second time period, which may not coincide with the first timeperiod. The first time period may be synchronized among all devices in aplurality of dynamic spectrum access networks, each of which may benon-cooperative with each of the other networks. The device also mayschedule a first plurality of time periods at regularly-spaced timeintervals during which the device refrains from transmitting, which maybe synchronized with the other DSA-enabled devices. The device also mayrepeat sensing during each of a second plurality of time periods, eachof which may not coincide with any of the first time periods. The secondtime periods may be scheduled to have random time intervals betweenadjacent periods. During the first time period, at least one of theplurality of DSA-enabled devices may actuate a detector to detectnon-cooperative spectrum use. The first time period may be synchronizedamong substantially all DSA-enabled devices in a geographic region, andmay occur at different points in adjacent communication frames. Each ofthe plurality of devices may include a third circuit to sense at leastone channel to detect cooperative spectrum use during a third timeperiod selected by the device, which may not coincide with the firsttime period. Each of the second and/or third circuits may include adetector.

According to an aspect of the invention, a method of coordinatingcommunication among a plurality of devices in a network may include, ata first of the plurality of devices: detecting spectrum use in aplurality of channels, based on the detected spectrum use, selecting acommunication channel, and transmitting an initial communication packeton the selected channel, and, at a second of the plurality of devices:receiving the communication packet; and responding to the initialcommunication packet. The method also may include, by at least one ofthe plurality of devices, periodically measuring spectrum use of theselected channel, and, responsive to detecting spectrum use identifiedas likely to cause interference to a non cooperative device, sending anindication thereof to the first device, the second device, or both. Eachof the devices may be a dynamic spectrum access-enabled device, and maybe capable of communicating on a plurality of channels afterinitialization of communication among the plurality of devices. Thedevices may not be primary devices with respect to the plurality ofchannels. The selected channel may not be reserved for use by the DSAnetwork in a regulatory scheme, and may be reserved for use by a primarynetwork in a regulatory scheme. The second of the plurality of devicesmay receive a communication packet from a non-cooperative device, selectthe communication channel based on an identifier in the communicationpacket received from the first of the plurality of devices, and send theresponse to the initial communication packet on the communicationchannel. The second device also may receive spectrum use information forat least one of the plurality of channels from at least the second ofthe plurality of devices, and select the communication channel furtherbased on the received spectrum use information. The initialcommunication packet may include an indication of the selected channel.Each of the first and second devices may operate as a base station or asubscriber unit.

A system according to an aspect of the invention may include a firstdevice configured to detect spectrum use in a plurality of channels,based on the detected spectrum use, select a communication channel, andtransmit an initial communication packet on the selected channel; and asecond device configured to receive the communication packet, andrespond to the initial communication packet. One or both of the devicesmay periodically measure spectrum use of the selected channel, and,responsive to detecting spectrum use identified as likely to causeinterference to a non-cooperative device, send an indication thereof tothe other device.

According to an aspect of the invention, a method of coordinatingcommunication among a plurality of dynamic spectrum access (DSA)-enableddevices in a DSA-enabled network may include, at a first of theplurality of devices: detecting spectrum use in a plurality of channels,based on the detected spectrum use, generating a candidate channel listidentifying channels suitable for use by the DSA-enabled devices in theDSA-enabled network, selecting a communication channel from thecandidate channel list, and transmitting an initial communication packeton the selected channel, where the initial communication packetidentifies the first of the plurality of devices as a cooperative devicefor the DSA-enabled network. The selected channel may not be reservedfor use by the DSA-enabled network in a regulatory scheme, and may bereserved for use by a primary network in a regulatory scheme. The methodalso may include receiving a packet from a second device in theDSA-enabled network, that indicates that the selected channel isunsuitable for use by the DSA-enabled network, sending a secondcommunication packet to other devices in the DSA-enabled network,receiving channel preference data from at least one other device in theDSA-enabled network, based on the channel preference data, selecting anew communication channel, and sending a third communication packet onthe new communication channel.

According to an aspect of the invention, a device suitable for use in adynamic spectrum access (DSA)-enabled network may include acommunication coordinator to manage communication with a cooperativedevice, the communication coordinator including an initialization moduleconfigured to identify use of a first communication channel by acooperative device based on detected spectrum use in a region, a channelmaintenance module configured to initialize and maintain communicationwith the cooperative device on the first channel, and a channelswitching module configured to cause the device to stop using the firstchannel to communicate with the cooperative device and begin using asecond channel to communicate with the cooperative device, where thecommunication coordinator may activate each of the initializationmodule, the channel maintenance module, and the channel switching modulebased on a communication received from the at least one othercooperative device. The communication coordinator may activate thechannel switching module in response to a communication received fromthe cooperative device which indicates the presence of non-cooperativespectrum use, a communication received from the cooperative device whichindicates the cooperative device is going to switch channels to achannel not usable by the device, or a combination thereof. The secondchannel may not be reserved for use by the device in a regulatoryscheme, and may be reserved for a primary network in a regulatoryscheme.

According to an aspect of the invention, a method of communicating withat least one cooperative device may include detecting use of a firstcommunication channel by the at least one cooperative device based ondetected spectrum use in a region, initializing and maintainingcommunication with the at least one cooperative device on the firstcommunication channel, and ceasing communication with the at least onecooperative device on the first communication channel and initializingcommunication with the at least one cooperative device on a secondcommunication channel selected based on data describing non-cooperativeuse of the second communication channel. The method may includereceiving a communication from the cooperative device indicatingnon-cooperative use of the first communication channel, and ceasingcommunication with the cooperative device in response to thecommunication. The method also may include receiving a communicationfrom the at least one cooperative device indicating the device is goingto switch channels to an unusable channel, and detecting use of a firstcommunication channel in response to receiving the communication.

According to an aspect of the invention, a method of classifying thestatus of a channel by a dynamic spectrum access-enabled device mayinclude determining a channelization for a region of spectrum, measuringthe energy present in a plurality of channels defined by thechannelization, generating a first confidence score indicating thedifference between a predefined signal mask and energy levels measuredin a first group of the plurality of channels, generating a secondconfidence score indicating the difference between the predefined signalmask and energy levels measured in a second group of the plurality ofchannels including at least one channel at a higher frequency than eachchannel in the first group of channels, and, in response to at least oneof the first and second confidence scores exceeding a predefinedthreshold, classifying the corresponding group of channels as containinga cooperative signal. The method also may include classifying thecorresponding group of channels as containing a dynamic spectrum accesssignal. The first and second group of channels may have zero, one, ormore channels in common. The frequency range encompassed by the firstand second group of channels may correspond to a predefinedchannelization. The channelization may be different than achannelization associated with a non-cooperative signal expected in theregion of spectrum.

According to an aspect of the invention, a method of operating a dynamicspectrum access-enabled device may include determining a channelizationfor a region of spectrum, measuring energy present in at least onechannel defined by the channelization, based on the measured energy,identifying a signal in the at least one channel, comparing the detectedsignal to a predefined signal mask that defines a power-frequencyrelationship for a modeled signal in the at least one channel,calculating a confidence score based on the comparison of the detectedsignal to the signal mask that indicates the likelihood that the signalis a cooperative signal, and based on the confidence score, classifyingthe signal identified in the at least one channel as at least one of anon-cooperative signal, a primary signal, and a cooperative signal. Thechannelization may be different than a channelization associated with anon-cooperative signal expected in the region of spectrum. The methodmay include communicating with a cooperative device on the at least onechannel. The method also may include identifying a known non-cooperativesignal bandwidth corresponding to a region of spectrum that includes theat least one channel, and selecting the signal mask to have a bandwidthdifferent than the non-cooperative signal bandwidth. The method mayinclude identifying the type of signal detected in the at least onechannel as being a type expected for a cooperative signal. The methodalso may include, prior to identifying the signal in the at least onechannel, measuring noise occurring in the channel for a period of time,and reducing the value of the measured energy used to identify thesignal in said identifying step based on the noise measured during theperiod of time. Calculating the confidence score further may includecalculating the difference in mean values between the signal mask andthe detected signal in one or more pass-bands, calculating thedifference in mean values between the signal mask and the detectedsignal in one or more stop-bands, calculating the difference in thevariance between the signal mask and the detected signal in one or morepass-bands, calculating the difference in the variance between thesignal mask and the detected signal in one or more stop-bands,calculating the distance between the amplitude of the center pass-bandof the detected signal and the side guard-bands of the detected signal,and calculating the difference between the calculated distance and thedistance between the amplitude of the center pass-band of the signalmask and the side guard-bands of the signal mask, calculating thedifference between the peak-to-mean ratio of the signal mask and thepeak-to-mean ratio of the detected signal, or any combination thereof.

An aspect of the invention may include a detector configured to measureenergy present in at least one channel, a first circuit to identify asignal in the channel based on the energy measured by the detector,compare the detected signal to a predefined signal mask that defines apower-frequency relationship for a modeled signal in the at least onechannel, calculate a confidence score based on the comparison of thedetected signal to the signal mask, the confidence score indicating thelikelihood that the signal is a cooperative signal; and, based on thecalculated confidence score, classify the signal identified in the atleast one channels as available for use by the device node. The devicemay include a signal classifier. The detector may measure energy presentin at least one of a first side portion and a second side portion of anarrow channel, the first side portion being defined by a firstfrequency range and the second side portion being defined a secondfrequency range, the second frequency range being higher than andnon-overlapping with the first frequency range. The device may include asecond circuit to define an energy threshold equal to the measuredenergy level, measure energy present in a central portion of the narrowchannel, the central portion being defined by a central frequency rangebetween the first and second frequency ranges and, if the energymeasured in the central portion is at least as great as the threshold,classify a signal detected in the narrow channel as a cooperativesignal. Such a device may include a second circuit to determine theavailability of the at least one channel for use by the device based onsignal classification data received from the first circuit. The devicemay include a policy module to specify how often the detector measuresenergy in the at least one channel. The device may be a secondary devicein the channel, and may be a base station or a subscriber unit.

An aspect of the invention includes a method of identifying acooperative signal by a dynamic spectrum access-enabled device, whichmay include measuring energy present in at least one of a first sideportion and a second side portion of a narrow channel, the first sideportion being defined by a first frequency range and the second sideportion being defined a second frequency range higher than andnon-overlapping with the first frequency range, setting an energythreshold to be the value of the energy measured in said side portionmeasuring step, measuring energy present in a central portion of thenarrow channel, the central portion being defined by a central frequencyrange between the first and second frequency ranges, and, if the energymeasured in the central portion is at least as great as the threshold,classifying a signal detected in the narrow channel as a cooperativesignal. The narrow channel may be defined by a channelization differentthan a channelization associated with a non-cooperative signal expectedin a region of spectrum that includes the narrow channel. The method mayinclude communicating with a cooperative device on the narrow channel.The method also may include, prior to classifying the signal as acooperative signal, measuring noise occurring in the channel for aperiod of time, and reducing the value of the measured energy used toidentify the signal in said classifying step based on the noise measuredduring the period of time.

Additional features, advantages, and embodiments of the invention may beset forth or apparent from consideration of the following detaileddescription, drawings, and claims. Moreover, it is to be understood thatboth the foregoing summary of the invention and the following detaileddescription are exemplary and intended to provide further explanationwithout limiting the scope of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, are incorporated in and constitute apart of this specification; illustrate embodiments of the invention andtogether with the detailed description serve to explain the principlesof the invention. No attempt is made to show structural details of theinvention in more detail than may be necessary for a fundamentalunderstanding of the invention and various ways in which it may bepracticed.

FIG. 1A shows an example DSA-enabled device according to an embodimentof the invention.

FIG. 1B shows an example DSA-enabled device and an example informationflow according to an embodiment of the invention.

FIG. 2 shows an example logical framework for a DSA-enabled deviceaccording to an embodiment of the invention.

FIG. 3 shows an example process for communicating in a DSA systemaccording to an embodiment of the invention.

FIG. 4A is a schematic of an example DSA network topology according toan embodiment of the invention.

FIG. 4B is a schematic of an example DSA network topology according toan embodiment of the invention.

FIG. 4C is a schematic of an example DSA network topology according toan embodiment of the invention.

FIG. 4D shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.

FIG. 4E shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.

FIG. 4F shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.

FIG. 5 shows an example system flow diagram for a DSA-enabled deviceperforming a concurrent scanning and communication process according toan embodiment of the invention.

FIG. 6 shows an example system flow diagram for a DSA-enabled deviceperforming a concurrent scanning and communication process according toan embodiment of the invention.

FIG. 7 is an illustration of various regions of spectrum utilized by aDSA system according to an embodiment of the invention.

FIG. 8 shows an example spectrum plan that omits the cellular band andportions of unlicensed, radar, and government bands from considerationfor use by a DSA system according to an embodiment of the invention.

FIG. 9 shows examples of band-specific sensing requirements and detectorrequirements according to embodiments of the invention.

FIG. 10 shows an example spectrum plan using channel categories toschedule detector operations during an arbitrary window of timeaccording to an embodiment of the invention

FIG. 11 shows an example of channel use table modification according toan embodiment of the invention.

FIG. 12. shows an example data flow within a DSA-enabled device relatedto modifying a channel use table according to embodiments of theinvention.

FIG. 13. shows an example data flow within a DSA-enabled device relatedto modifying a channel use table according to embodiments of theinvention.

FIG. 14 shows an example allocation of sensing time periods according toan embodiment of the invention.

FIG. 15A shows an example message sequence diagram for an interactionbetween a scheduler and other DSA-enabled device components according toan embodiment of the invention.

FIG. 15B shows an example message sequence diagram for an interactionbetween a scheduler and other DSA-enabled device components according toan embodiment of the invention.

FIG. 16 shows operation timelines for two DSA-enabled devices operatingduring a time span in which each DSA-enabled device has variousdetection periods and transmission/reception periods.

FIG. 17 shows operation timelines for two DSA-enabled devices with acoordinated detection period according to an embodiment of theinvention.

FIG. 18 shows operation timelines for two DSA-enabled devices withcoordinated and uncoordinated detection periods according to anembodiment of the invention.

FIG. 19 shows an example high-level view of a DSA channel selection andmaintenance process according to an embodiment of the invention.

FIG. 20 is a block diagram of an example communication coordinatoraccording to an embodiment of the invention.

FIG. 21A shows an example process flow for a base station in a startupmode according to an embodiment of the invention.

FIG. 21B shows an example process flow for a base station in a channelmaintenance mode according to an embodiment of the invention.

FIG. 21C shows an example process flow for a base station in a channelswitching mode according to an embodiment of the invention.

FIG. 21D shows an example process flow for a subscriber DSA-enableddevice in a startup mode according to an embodiment of the invention.

FIG. 21E shows an example process flow for a subscriber DSA-enableddevice in a channel maintenance mode according to an embodiment of theinvention.

FIG. 21F shows an example process flow for a subscriber DSA-enableddevice in a channel switching mode according to an embodiment of theinvention.

FIG. 22A shows an example process flow for a base station during acommunication coordination process according to an embodiment of theinvention.

FIG. 22B shows an example process flow for a subscriber DSA-enableddevice during a communication coordination process according to anembodiment of the invention.

FIG. 23A shows an example communication flow between a base station anda subscriber DSA-enabled device during a startup sequence according toan embodiment of the invention.

FIG. 23B shows an example communication flow between a base station anda subscriber DSA-enabled device during channel maintenance according toan embodiment of the invention.

FIG. 23C shows an example communication flow between a base station anda subscriber DSA-enabled device during channel switching initiated by asubscriber DSA-enabled device according to an embodiment of theinvention.

FIG. 23D shows an example communication flow between a base station anda subscriber DSA-enabled device during channel switching initiated by abase station according to an embodiment of the invention.

FIG. 24A shows a schematic illustration of a multi-cluster networkaccording to embodiments of the invention.

FIG. 24B shows a schematic illustration of a multi-cluster networkaccording to embodiments of the invention.

FIG. 24C shows an example network diagram of unsynchronized DSA-enablednetworks and associated convergence behavior according to an embodimentof the invention.

FIG. 24D shows an example network diagram of synchronized DSA-enablednetworks and associated convergence behavior according to an embodimentof the invention.

FIG. 24E shows an example network diagram of a DSA-enabled network thatincludes multiple clusters according to an embodiment of the invention.

FIG. 25 illustrates a sample DSA 2 MHz channel and its division into 25kHz slivers according to an embodiment of the invention.

FIG. 26 shows an example process used by a signal classifier accordingto an embodiment of the invention.

FIG. 27 shows a sample signal mask comparison according to an embodimentof the invention.

FIG. 28 shows a sample signal mask according to an embodiment of theinvention.

FIG. 29 shows a sample of a narrowband signal analyzed by a classifieraccording to an embodiment of the invention.

FIG. 30 shows a schematic illustration of overlapping scanning windowsaccording to embodiments of the invention.

FIG. 31 shows a block diagram of a policy module according to anembodiment of the invention.

FIG. 32 shows an example process for obtaining approval from a policymodule according to an embodiment of the invention.

FIG. 33 shows an example process for using policies according to anembodiment of the invention.

FIG. 34A shows an example logical flow for applying policy requirementsto channel use tables according to an embodiment of the invention.

FIG. 34B shows an example logical flow for applying policy requirementsto an example channel use table according to an embodiment of theinvention.

FIG. 35 shows a schematic view of a radio driver architecture thatsupports queuing according to an embodiment of the invention.

FIG. 36 shows an example DSA receiver RF circuit according to anembodiment of the invention.

FIG. 37 shows an example DSA transmitter RF circuit according to anembodiment of the invention.

FIG. 38 shows a schematic view of a digital processing board used in aDSA system according to an embodiment of the invention.

FIG. 39 shows a schematic diagram of functionality implemented by adigital processing board in a DSA system according to an embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the invention is not limited to the particularmethodology, protocols, topologies, etc., as described herein, as thesemay vary as the skilled artisan will recognize. It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the invention. It also is to be noted that as used herein andin the appended claims, the singular forms “a,” “an,” and “the” includethe plural reference unless the context clearly dictates otherwise.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which the invention pertains. The embodiments of theinvention and the various features and advantageous details thereof areexplained more fully with reference to the non-limiting embodimentsand/or illustrated in the accompanying drawings and detailed in thefollowing description. It should be noted that the features illustratedin the drawings are not necessarily drawn to scale, and features of oneembodiment may be employed with other embodiments as the skilled artisanwould recognize, even if not explicitly stated herein.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least two units between any lower value and anyhigher value. As an example, if it is stated that the concentration of acomponent or value of a process variable such as, for example, size,angle size, pressure, time and the like, is, for example, from 1 to 90,specifically from 20 to 80, more specifically from 30 to 70, it isintended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32etc., are expressly enumerated in this specification. For values whichare less than one, one unit is considered to be 0.0001, 0.001, 0.01 or0.1 as appropriate. These are only examples of what is specificallyintended and all possible combinations of numerical values between thelowest value and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

Particular methods, devices, and materials are described, although anymethods and materials similar or equivalent to those described hereincan be used in the practice or testing of the invention. All referencesreferred to herein are incorporated by reference herein in theirentirety.

Moreover, provided immediately below is a “Definition” section, wherecertain terms related to the invention are defined specifically and useof these terms in the specification and the claims have the meaningsascribed herein. Particular methods, devices, and materials aredescribed, although any methods and materials similar or equivalent tothose described herein can be used in the practice or testing of theinvention. All references referred to herein are incorporated byreference in their entirety.

DEFINITIONS

Unless indicated otherwise, as used herein and in the appended claims,the following terms have the meanings ascribed below:

the term “channel” refers to a logical channel, which may include one ormore physical channels or frequencies. Typically, a logical channel canbe mapped to a communication frequency or a set of communicationfrequencies used to communicate among devices that use the channel. Achannel typically is defined as a range of frequencies (e.g. 900-910Mhz). “Channelization” refers to the definition of one or more channelswithin a defined spectrum range. A channel may be described as in use oroccupied if at least one frequency in the channel is in use by a device,or if a signal is otherwise detected in at least one frequency in thechannel. The term “center frequency” may be used to refer to a frequencyat or near the center of a logical channel. Thus, a channel also may bespecified in terms of a center frequency and channel width.

“Dynamic Spectrum Access” (DSA) refers to the process of communicatingon one or more channels which are selectable subsequent toinitialization of communication between two devices. Typically a DSAprocess may use regions of spectrum to which the devices do not havepriority use rights, i.e., the devices may not be primary devices, ormay not be providing a primary use of the region of spectrum. A DynamicSpectrum Access-enabled (“DSA-enabled”) device is a device that iscapable of communicating with one or more other DSA-enabled devicesusing a dynamic spectrum access process. Typically, DSA-enabled devicescan autonomously assess the radio spectrum environment, and mayautomatically select a communication channel based on capacity,interference, and/or other conditions. A DSA-enabled device also may bereferred to herein as a DSA node. DSA-enabled devices typically operatewithin the radio frequency (RF) regions of the electromagnetic spectrum.

Two DSA-enabled devices are described herein as “cooperative” devices ifthey engage in communication and channel switching among identifiedavailable channels. A DSA-enabled device that is not engaging incommunication with another DSA-enabled device may be described herein as“non-cooperative” with the other DSA-enabled device. Thus, two DSAnetworks may overlap in channel use without the members of each networkbeing considered as “cooperative” with members of the other network.Non-cooperative DSA-enabled devices typically do not exchangecommunication data, but may share or exchange control data, such as whennon-cooperative DSA networks in a geographic region are configured touse a synchronized detection gap. A DSA signal or device may further beclassified as cooperative or non-cooperative. A non-DSA-enabled deviceor signal may be described as non-DSA and/or non-cooperative. That is, adevice may be incapable of performing, or not configured to perform,dynamic spectrum allocation, but also may be described asnon-cooperative. Thus, in some contexts the term “non-cooperative” mayencompass a non-DSA-enabled device. For example, a signal detected on achannel may be classified initially as DSA or non-DSA. An unclassifiedsignal may be treated and described as a non-DSA signal unless and untilit is classified otherwise. A “DSA signal” refers to a transmission sentby or identified as sent by a DSA-enabled device, whether cooperative ornon-cooperative. A signal may be described as “cooperative” or“non-cooperative” based on whether it was sent by or identified as sentby a cooperative or non-cooperative DSA-enabled device, respectively. A“non-cooperative signal” also may refer to a signal from anon-DSA-enabled device.

The term “detector” refers to a sensor capable of sensing energy at oneor more frequencies. A detector typically includes a hardware sensor andadditional software, hardware, or both to perform additional processingof received or sensed transmissions. Various detectors are describedherein. Unlike a receiver, a detector typically does not demodulate orotherwise extract information from received energy, such as informationcontained in a signal sent on a channel. A detector may calculate orinfer information about the energy itself, such as amplitude andfrequency at which the energy is detected. A detector may also bereferred to as a “sensor.”

The term “detection distance” or “detection radius” refers to thedistance at which a detector is capable of detecting a transmission orat which it is believed that a detector is capable of detecting atransmission.

The term “detection gap” or “gap” refers to a synchronized time periodduring which DSA-enabled devices in a DSA network refrain fromtransmitting, which may allow for more efficient or successfulenvironmental sensing. The detection gap also may be referred to as a“quiet period.” Typically, one or more devices in a DSA-enabled networkmay perform detection during this period.

The term “interference distance” refers to the distance at which adevice may interfere with the operation of another device or thetransmission/reception of another device, or at which it is believedthat the device may interfere with the operation of another device orthe transmission/reception of another device.

A “primary” device, network, operator, or other entity is one that has apriority right to a portion of the spectrum relative to another device,network, operator, or other entity. Similarly, a “primary” spectrum usehas a priority right to a portion of spectrum relative to another use ofthe spectrum. A lower-priority entity may be referred to as “secondary,”and a lower-priority use may be referred to as a “secondary use.” Alicensee of a particular region of spectrum in a regulatory schemetypically is a primary user. A single entity or use may be primary toone entity or use but secondary to another. A “co-primary” or“co-secondary” device, network, operator, use, or other entity is onethat has the same right to operate in a portion of the spectrum asanother respective co-primary or co-secondary device, network, operator,use, or other entity. Typically, neither device may cause harmfulinterference to the other and, in certain cases, they must acceptharmful interference from each other. For example, a regulatory schememay assign a hierarchy of licensees or uses for a particular region ofspectrum, or may allocate or assign spectrum for certain primary,co-primary, secondary, co-secondary, or unlicensed use (or combinationsthereof) within a geographic region.

The term “maximum interference free transmit power” (MIFTP) refers to adetermined power level that can be transmitted by a DSA-enabled devicewithout exceeding interference requirements for non-cooperativetransmission sources or other DSA-enabled devices, such asnon-cooperative DSA-enabled devices, that utilize the same portion ofwireless spectrum. Interference requirements may include metrics such asthe interference-to-noise-ratio, probability of interference occurrence,and other metrics.

The terms “module” and “circuit” refer to a device or device componentthat performs one or more logically-related functions. A module orcircuit may include any combination of hardware and/or software, or bothhardware and software, and may implement one or more logical processes.

The term “rendezvous” refers to a process of multi-frequency neighborand network discovery and ongoing negotiation of one or more controland/or data channels among multiple DSA-enabled devices.

The terms “wideband” and “narrowband” refer to signals, detectors, orportions of spectrum that are relatively wide or narrow, respectively.The particular division between wideband and narrowband may varysomewhat depending on the specific region of spectrum or use case beingconsidered, as will be understood by one of skill in the art. Inembodiments of the invention, a narrowband signal typically is anysignal of about 1 MHz or less, and a wideband signal typically is anysignal requiring more bandwidth. Signals, detectors, or other devicesmay operate in a sub-region of a narrow- or wideband region of spectrum.For example, an illustrative wideband detector may detect signals up to20 MHz wide with a 20 kHz resolution bandwidth. It will be understoodthat other ranges and configurations may be used. For example, in someembodiments a “narrowband” signal or region may refer to a signalsufficient to contain a particular type of data, such as where 4 kHznarrowband channels or signals correspond to voice transmissions, andlarger wideband signals correspond to greater amounts of data.

A “DSA-enabled network” or “DSA network” refers to a network ofDSA-enabled devices that operate “cooperatively.”

An “ad-hoc” network is a network that does not have a pre-plannedtopology, and/or one that uses a non-static, dynamically-selectable basestation or other central controller.

A “peer-to-peer” network is a network that does not use any base stationor other central controller. In some configurations, one or moreDSA-enabled devices in a “peer-to-peer” network may perform some or allof the functions associated with a central controller in anon-peer-to-peer network.

An “infrastructure” network is a network that uses a base station orother central controller.

The term “local” may refer to a module, device, component, circuit, ordata that is integral to an individual DSA-enabled device or otherdevice. For example, each DSA-enabled device in a DSA-enabled networkmay include a local detector that is used by the device. Similarly, eachDSA-enabled device may maintain a local set of ranked channels or otherdata.

Wireless spectrum is in increasing demand for a variety of consumer,corporate, government, military, and other uses. Since the amount ofspectrum is limited, regulatory schemes are commonly used to allocatespectrum to particular uses or licensees. Such schemes may beinefficient since, for example, a particular license or use may notefficiently or fully utilize all of the allocated and assigned spectrum.For example, communication resources may be modeled as athree-dimensional space with axes of space/beam angle, time, andfrequency. These three-dimensional communications resources representthe entirety of the resource available to satisfy the demands of legacycommunications systems and also the escalating demands of highly mobile,wide band communications services.

Using conventional spectrum allocation and assignment techniques, theremay not be sufficient spectrum available to satisfy all emergingdemands. However, as previously mentioned, relatively large sub-spacesof the communications resources space remain unused; major reservedspectral slots either are not utilized at all, or are grosslyunderutilized.

Methods, devices, and systems according to embodiments of the inventionmay allow for more efficient use of the RF spectrum. Embodiments maydynamically and efficiently distribute the communications resources(i.e., volumetric elements of the three-dimensional communicationsresource space) to multiple legacy uses as well as to evolving wide bandcommunications services for mobile users, by using dynamic spectrumaccess (DSA) techniques in which communication resources may be assignedduring operation of one or more communication systems, includingDSA-enabled systems. Specifically, embodiments may include the followingtwo main features or elements:

1. Local “hole” sensing (or monitoring) and local adaptation techniquesthat enable individual DSA-enabled devices to identify availablecommunications resources without causing interference. That is,DSA-enabled devices may identify unused portions of the communicationsresources space (i.e. unused regions of frequency, spatial/angle, and/ortime).

2. Network-based resource allocation and media access control (MAC)functionality may dynamically route incoming message traffic throughstable frequency, spatial/angle, and time holes.

In some embodiments, the first element (local “hole” sensing/monitoringand local adaptation) may be accomplished using various types ofdeterminations, such as: (a) propagation loss between cooperativeDSA-enabled devices; (b) maximum allowable transmit power; (c) beamangles required to restrict interference with other users to, at most, acertain threshold level; and (d) spectrum occupancy. In variousembodiments, passive and active sensing techniques may be used to makethese determinations, as described in further detail below. The systemmay use measurements at each DSA-enabled device and/or active probingtechniques to locally and adaptively determine the frequencies, beamangles, and/or power levels available to each DSA-enabled device. Insome embodiments, much or all of the decision logic regarding availableand/or preferred communication channels is within each DSA-enableddevice.

In some embodiments, the second element (resource allocation and MACfunction) may be addressed through several sub-features: (a) decidingwhat information needs to be sent and to whom; (b) optimizing frequencyassignments, transmit power levels, time slots, routes, and/or otheraspects of communication among DSA-enabled devices; and (c) coordinationof time slot and frequency decisions locally. It has been found thatwhen allowable spectrum choices dynamically vary within local groups,large amounts of spectrum may be found that are locally stable anduniform.

Embodiments of the invention may be implemented over a broad range ofscenarios, such as terrestrial, airborne, training, low and highcapacity links, denial-of-service scenarios, and other situations. Someembodiments may perform DSA techniques using a radio that operates witha relatively low transmit power, and/or in early-entry situations withminimal advanced planning and constant network changes (networktopology, traffic flow and volume, and network size). Embodiments may behighly robust, fault tolerant, have simple user interfaces, and may becompatible with existing uses and systems.

According to embodiments of the invention, a Dynamic Spectrum Access(DSA) network may use one or more DSA-enabled devices that canautonomously assess the radio spectrum environment; and mayautomatically (i.e., without human intervention) adjust communicationchannels used by the DSA-enabled devices based on various capacity,interference, and other conditions. A DSA-enabled device may use aportion of spectrum that is assigned for use by, or that may be in useby another systems or network. The DSA-enabled device may seek to avoidor minimize interference with other wireless signals in a spectralregion used by the DSA system.

FIGS. 1A and 1B show examples of DSA-enabled devices and example dataflows according to embodiments of the invention. In some embodiments, aDSA-enabled device 100 may include four main components: an environmentsensing and detection module 110; a DSA engine 120; a radio or othercommunications module 150, and a policy module 140.

The environmental sensing module 110 may monitor or sample a portion ofspectrum, such as a range of frequencies defined by a set of logicalchannels, to determine whether the portion of spectrum is in use. One ormore local detectors 112 may be used to measure energy across channels.Various types of local detectors may be used, including widebanddetectors, narrowband detectors, application-specific detectors such asdetectors configured to specifically detect television, cellular,wireless microphone, or other specific signals, and any other suitabledetector. The environmental sensing module may include a distributeddetection coordinator 116 to manage the distribution and receipt ofdistributed environmental sensing information among one or moreDSA-enabled devices, such as when Group Behavior—type techniques ordistributed sensing techniques are used. The environmental sensinginformation may include, for example, an indication of energy and/orsignals detected by each DSA-enabled device in one or more channels. Thedistributed detection coordinator 116 also may manage low-level securityinformation between the DSA-enabled devices when these devices exchangesensor data. The environmental sensing module also may include a probesignal module 114 to coordinate sending/receiving probe signals that areused to identify signal propagation characteristics between DSA-enableddevices in a DSA network. The environmental sensing module 110 mayprovide environmental sensing information (also called detection data)to the DSA engine module 120, including radio frequency (RF) environmentinformation such as energy levels, specific signal types and strengths,power levels and structures of signals in a region of spectrum detectedby the local detectors, environmental sensing information received fromother cooperative devices, signal propagation data, and any otherenvironmental data detectable by the DSA-enabled device. Theenvironmental sensing module may receive control inputs from the DSAengine module 120 that specify when and upon which portions of thespectrum the local detectors 112 are utilized, when the probe operates,and how cooperative sensing information is collected, reported, andsecured. In some embodiments, some DSA-enabled devices in a system ornetwork include detectors, while other DSA-enabled devices do notinclude or use a detector. In such a configuration, the DSA-enableddevices which include detectors may provide spectrum usage informationto the other DSA-enabled devices that do not have detectors. Externalspectrum measurement systems also may be used. For example, one or moredetectors that are not DSA-enabled devices or are not in a DSA-enablednetwork may gather and distribute spectrum information to theDSA-enabled devices, which may or may not include detectors.

A DSA-enabled device typically may perform environmental sensing,including detection of other signals, at a separate time from when itperforms routine transmission and reception of data and controlinformation. This may allow the automatic gain control (AGC) and/orother receiver parameters to be optimized for detection independentlyfrom data reception. In some configurations, sensing may take placeduring the reception of data if there are two simultaneous data paths tothe radio or other transceiver and to the detector and if the detectorbandwidth is greater than the bandwidth of the received signals. In thiscase, detection sensitivity may be reduced when DSA transmissions arereceived during a time period when the DSA-enabled device is in a modeconfigured to detect transmissions from non-DSA sources.

The DSA engine module 120 may comprise several components, such as aspectrum manager 130; a communication coordinator 124; and a high-levelscheduler 122. Within each DSA-enabled device, the scheduler 122 maymanage operation of the detectors. The channel manager 132 may generateand maintain a list of candidate channels available for use by theDSA-enabled device. The communication coordinator 124 may use channelsidentified by the spectrum manager for network discovery and frequencynegotiation with other cooperative DSA-enabled devices. The operation ofthese components and subsystems is described in further detail below.

According to embodiments of the invention, a DSA-enabled device maysupport concurrent connections to a plurality of DSA-enabled networks.In an example embodiment, the DSA-enabled device may simultaneously joinmultiple DSA-enabled networks by maintaining separate instances ofrendezvous state, channel control lists, policy information, and anyother information related to each DSA-enabled network. A collection ofsuch information specific to an individual DSA-enabled network or acluster of DSA-enabled nodes is called a DSA-enabled network context.The number of different DSA-enabled networks that a specific DSA-enableddevice may join may be limited by the amount of memory available in thedevice to store DSA-enabled network contexts.

The DSA-enabled device may select a DSA-enabled network context tocomplete a specific operation with respect to a specific DSA-enablednetwork and/or cluster. For example, a DSA-enabled device may maintain afirst set of DSA-enabled network information corresponding to a firstDSA-enabled network, and use that set of information for managing thefirst DSA-enabled network. It also may maintain, a second set ofDSA-enabled network information for a second DSA-enabled network, athird set for a third network, and so on. In other embodiments, aDSA-enabled device may maintain a single context.

The DSA engine module may coordinate communications between theDSA-enabled device and other cooperative DSA-enabled devices. One aspectof this coordination may be the association of each action of theDSA-enabled device with a specific context. For example, the DSA enginemodule may receive information from the environmental sensing moduleregarding the radio frequency (RF) environment observed by theDSA-enabled device, environment information observed by theenvironmental sensing modules of other cooperative DSA-enabled devices,and similar data, and then use this data for classification,interference avoidance, and channelization of the spectrum for use bythe DSA-enabled device. The classification, interference avoidance, andchannelization may be applied with respect to a DSA-enabled networkcontext.

The DSA engine module also may include a scheduler 122 to coordinatetransmitting, receiving, and sensing times. For example, the schedulermay define various times in each frame during which the DSA-enableddevice performs different operations, such as sending and receiving dataand/or control information using the radio 150, making observationsabout spectrum usage using the environmental sensing module 110 (andremote environmental sensing modules of other cooperating DSA-enableddevices), and performing analysis of RF environment information andsignals observed by the DSA-enabled device. The scheduler 122 may bepart of or controlled by the DSA engine module, or it may be a separatemodule within the DSA-enabled device.

The DSA engine module may include or control a spectrum manager 130 toanalyze signals or potential signals for which information is obtainedby the DSA-enabled device, analyze spectrum usage, and identifypotential channels for use by the radio. For example, the spectrummanager may include one or more signal classifiers 134 and a channelmanager 132. Each signal classifier 134 may receive some or all of theinformation from the sensing module 110, such as power levels andstructures of signals in a region of spectrum observed by the sensingmodule. A signal classifier may use various RF filters, signal masks,prior classification results, demodulation, and other analysistechniques to identify signals contained in the information provided bythe environmental sensing module. For example, a signal classifier maydiscriminate between cooperative signals, non-cooperative DSA signals,and non-cooperative non-DSA signals. In addition, the signal classifiermay store information about the classification process for later use bythe classification manager. This stored information is calledclassification results. Classification results may be used by aclassifier to “learn” classifications in order to reduce futureclassification errors, or to speed classification of previously viewedinformation. A signal classifier 134 may then send data describing thepresence or absence of signals and, if present, the types of signals invarious channels to the channel manager 132. For example, in anembodiment, a DSA-enabled device may store detection data andclassification results for later reuse or analysis, such as in adatabase used by the channel classifier. Such stored data may be used toreduce subsequent processing errors. As a specific example, if a signalclassifier incorrectly identifies a particular signal within datareceived from a detector, the stored classification results may bereferred to at a later point in time to prevent the classifier frommaking the same incorrect identification if the signal is detectedagain.

A signal classifier 134 also may detect a non-cooperative signal in achannel being used by the DSA-enabled device. In response, a signalclassifier 134 or spectrum manager 130 may send an immediate message,such as a request to change channels, to the communication coordinator124. The request may cause the communication coordinator to initiate achange in the channel used by the DSA-enabled device for communicationwith other cooperative DSA-enabled devices. Such requests and channelchange processes are described in further detail below.

The channel manager 132 may analyze channel data received from thesignal classifier to identify one or more available channels that may beavailable for use by the DSA-enabled device. For example, the channelmanager may assign a preference rating or other indication of thedesirability of using each channel to communicate with other cooperativeDSA-enabled devices. Various metrics may be applied based on what isknown about each channel. For example, channels which include lowerfrequencies may be preferred over those with higher frequencies;channels more likely to avoid interference with non-cooperativenon-DSA-enabled devices may be preferred over channels that may incursome interference with non-DSA and/or non-cooperative DSA-enableddevices, and channels having the least energy detected may be preferred.Other metrics and comparisons may be used to select one or morepreferred channel(s). The specific metrics used may be partially orwholly dictated by a policy data (for example, as provided by a policymanager as described herein). In some embodiments, the specific metricsmay be included, in whole or in part, within a spectrum plan, such asthe example spectrum plan 841 illustrated in FIG. 7, which is describedin further detail below. Once the channel manager 132 has identified alist of candidate channels and/or ranked some or all of the channelsthat may be available for use by the DSA-enabled device, a candidatechannel list may be generated. Each of these steps may be performedwithin the scope of a specific DSA-enabled network context, or may beperformed by the DSA-enabled device in a global context.

The candidate channel list generated by the channel manager 132 may beprovided to a communication coordinator. The communication coordinatorincludes one or more modules that perform negotiation, monitoring, andfrequency maintenance among DSA-enabled devices in a DSA network. Thesemodules and the associated process(es) may be referred to as arendezvous module and/or process. In some cases, the term “rendezvous”also may refer to initial discovery performed by a DSA-enabled device toinitially join a specific DSA-enabled network, such as where twoDSA-enabled devices are described as “attempting to rendezvous” orsimilar. The communication coordinator 124 may receive informationregarding the availability of channels for use by the DSA network fromthe channel manager and from other sources, such as other DSA-enableddevices in the DSA network. Based on this information, one or morechannels may be selected for use.

A DSA-enabled device also may include a policy module 140 to receive andstore policy information that may be provided to other modules in theDSA-enabled device. Policies may specify, for example, channels that theDSA-enabled device should prioritize for use or non-use, channel userestrictions such as maximum transmitting power, geographicrestrictions, and other restrictions or limitations on spectrum usage.Policy data may be used, for example, by the channel manager duringcreation of a candidate channel list, and/or by the communicationcoordinator as part of a channel management process between multipleDSA-enabled devices in a DSA network. The policy module also may includecomponents or sub-modules for manipulating, enforcing, or otherwisemanaging policies. A policy may be associated with specific contexts, ormay be generally provided for a DSA-enabled device.

A DSA-enabled device also may include one or more radios 150, which mayinclude one on more hardware transceivers or other communicationdevices. A transceiver may include an API that allows the communicationcoordinator to change the frequencies on which the transceiver operates.The API may also include media access control (MAC) layer functions suchas parameterization of frame rate, frame structure, transmitter power,and other similar capabilities. Typically, the communication coordinatormanages communication functions of the transceiver(s). Other componentsof the DSA-enabled device may coordinate operation of the transceiverswith the rest of the DSA-enabled device. For example, a data queuemanager 152 and/or a transceiver manager 154 may manage data sent andreceived by the transceivers. As another example, a transceiver manager154 may generate and coordinate an operating schedule of operation forthe radio 150 and one or more detectors, and may do so in conjunctionwith or instead of the scheduler 122. In some embodiments, a singletransceiver may be used for spectrum sensing as well as communicatingwith other DSA-enabled devices. In such an embodiment, differentcomponents may control the transceiver during times when it is used tosense spectrum and when it is used to communicate. In some embodiments,the transceiver manager provides a MAC interface to a transceiver. Inother embodiments, the transceiver itself provides the MAC interface.For example, the DSA engine 120 may provide instructions to a MAC (notshown) to change the channel on which the transceiver operates. The DSAengine also may provide the MAC with a list of channels and times onwhich to perform spectrum sensing, and the MAC may then control thespectrum sensing operation of the transceiver.

The environmental sensing module 110 may perform two main functions:detection of non-cooperative, non-DSA signals, and detection of otherDSA-enabled devices or DSA-enabled networks. By detectingnon-cooperative, non-DSA signals, a DSA-enabled device may reduce orminimize the potential for interference with the associated non-DSAsources. Detection of other DSA-enabled devices may allow theDSA-enabled device to join one or more DSA-enabled networks, and/or toavoid other, non-cooperative DSA-enabled devices and thus reduce orminimize mutual interference. For example, the environmental sensingmodule may provide data used to determine the maximum transmitting powerthe DSA-enabled device can or should use to limit harmful interferenceto other users of the spectrum to a specific amount, or to minimize oreliminate such interference. The detector information also may be usedby the spectrum manager and/or communication coordinator to identify andclassify other DSA signals. A higher sensitivity of detection may allowfor more accurate identification and classification of sensed signals,may enable the DSA-enabled device to transmit at higher power levelswithout causing interference, and may enable a DSA-enabled device tofind other DSA-enabled devices at greater distances.

Variations on the specific configurations described herein may be used.For example, various control channels and device architectures may beused. In some embodiments, DSA-enabled devices may use a channel onwhich the devices are communicating to exchange control messages. Inother embodiments, a separate and/or dedicated control or pilot channelmay be used to transfer control data between DSA-enabled devices.

Referring to FIG. 1B, an example process and data flow according toembodiments of the invention is shown by numbered steps 1-12. Theillustrated process may be used, for example, during a “cold start” of aDSA-enabled device, i.e., when a DSA-enabled device initially beginsoperation. At 1, a policy may be loaded from a policy module into apolicy validation agent or other component of the spectrum manager. At2, the policy may be read and validated, such as by a policy validationagent or other module, and policy data may be provided to the scheduler122. In some embodiments, the policy data is validated usingcryptographic means such as cryptographic hashes, digital signatures,and the like. The scheduler 122 may then identify one or more channelsto be sensed to the environment sensing module 110 at 3, In someembodiments, the DSA-enabled device may be configured to sense withincertain regions of spectrum or certain channels when first beginningoperation, i.e., at a cold start. For example, a DSA-enabled device maybe configured to search for other cooperative DSA-enabled devices in oneor more pre-set channels. The scheduler may receive detection data at 4.The detection data provided at 4 which is then provided to the signalclassifier 134 at 5. Alternatively, as previously described, detectiondata may be provided directly to the classifier 134. At 6, theclassifier 134 may identify specific signals and types of signalspresent in the detection data. The classifier may then provideinformation about identified signals to a channel manager'supdate/ranking module 132 at step 7, and at 8 the channels may be rankedaccording to their preference for use by the DSA-enabled device.Preferred and potential channels may be added to a candidate channellist at 9, which is then used by a rendezvous module at 10 to initiateand coordinate communication among DSA-enabled devices. At 11,information about potential and/or preferred channels may be provided tothe radio 150. The rendezvous module may then provide control data at 12to the DSA-enabled device, such as information received from otherDSA-enabled devices. The specific process shown in FIG. 1B isillustrative of the type used by embodiments of the invention, but itwill be understood that other processes may be performed, and more orfewer modules may be used than those specifically shown or described.Other steps may be performed. For example, a DSA-enabled device mayvalidate the integrity of the hardware and software that comprises thedevice. This may ensure that the DSA-enabled device (including hardwareand/or software) has not been tampered with. General tamper-resistantmethods of verifying hardware and software are well known to thoseskilled in the art. This verification may be performed, for example,prior to beginning the “cold start” process.

FIG. 2 shows an example software framework for a DSA-enabled deviceaccording to an embodiment of the invention. As can be seen by comparingFIGS. 1A and 1B to FIG. 2, many of the modules in the DSA-enabled devicemay correspond to or be implemented partially or entirely by varioussoftware components. For example, a spectrum manager may use channelclassifier, spectrum processor, channel manager, and other softwarecomponents as shown, which correspond to modules in the spectrum manager130. As a specific example, a spectrum processor may format detectordata into a format that allows for efficient use by the signalclassifier. It also may perform additional pre-processing tasks, such ascalculating a max hold array for data received from one or moredetectors and/or signal classifiers.

As previously described, in some embodiments a DSA-enabled device maystore detection data and classification results for later reuse oranalysis, such as in a data store 201. Such stored data may be used toreduce subsequent processing errors. As a specific example, if a signalclassifier incorrectly identifies a particular signal, the storedclassification results may be referred to at a later point in time toprevent the classifier from making the same incorrect identification ifthe signal is detected again.

The example software components may be implemented using a generalpurpose processor, or they may use specialty processors. A singleprocessor or other circuit may be used to implement multiple modules orfunctionality related to multiple modules, or multiple processors may beused. In a specific example embodiment, the DSA-enabled device, systemand policy APIs, internal APIs, and media access control (MAC) areimplemented using a general purpose processor, and the transceivermanager is implemented using a FPGA processor.

The system and policy APIs may provide programming interfaces outsidethe DSA-enabled device. For example, a web-based or other user interfacemay be used to access configuration, policy, or other files used by theDSA-enabled device via the API.

Internal APIs also may be used to allow for modification and/or re-useof common software tasks. For example, a detector API may be used toprovide a consistent interface to multiple detectors or types ofdetectors.

The individual modules shown in FIGS. 1A-1B and the related softwarecomponents of FIG. 2 are described in further detail below. It will beunderstood that although the functions of a DSA-enabled device and otheraspects of the invention are described herein with reference to variousmodules, specific functionality may be implemented in differentcombinations of hardware and software than specifically described foreach module without departing from the scope of the invention.

FIG. 3 shows an example of a basic process performed by one or moreDSA-enabled devices operating in a network according to an embodiment ofthe invention. At 310, one or more of the DSA-enabled devices mayperform environmental sensing to detect spectrum use and/oravailability. At 320, detected spectrum information may be used toclassify channels based on whether or not various signals were detectedin the channels. At 330, one or more DSA-enabled devices may generate alist of candidate channels suitable for use in communicating with otherDSA-enabled devices. Steps 310-330 may be repeated at various timeswhile the remainder of the illustrated process is performed, and whilethe DSA-enabled devices communicate within the network. At 340, one ormore DSA-enabled devices may then select an acceptable channel for usefrom the candidate channel list and proceed to communicate on one ormore selected channels at 350 or, if no further candidate channels areavailable, the device may return to 310 to attempt to identify anavailable channel. The channel selected at 350 may be selected usingvarious techniques. For example, a coordinating DSA-enabled device mayselect one or more acceptable channel(s) based on channel informationreceived from one or more cooperating DSA-enabled devices, such aschannel utilization channel preferences, non-cooperative channel use,and other environmental data. The coordinating DSA-enabled device maythen provide an indication of the selected channel(s) to cooperativeDSA-enabled devices Additional examples of techniques for selecting achannel are described with respect to FIGS. 21-22 herein. So long as noadverse condition is detected, the DSA-enabled device may continuecommunicating on the selected channels. When an adverse condition isdetected at 360, the DSA-enabled device may examine a current candidatechannel list and select one or more new channel(s) for use. The adversecondition may be detected by the DSA-enabled device or by anotherDSA-enabled device with which the first DSA-enabled device is incommunication. A new channel also may be selected for reasons other thanan adverse condition. As described in further detail herein, the stepsillustrated in FIG. 3 may be performed by one or more DSA-enableddevices in a DSA-enabled network, or may be performed by a combinationof devices, such as where a coordinating device makes determinationsregarding channel use based on data received from other devices in thenetwork.

DSA-enabled devices and DSA-enabled networks according to the inventionmay utilize and be used in various network topologies that use variousconfigurations and arrangements of DSA-enabled devices. In oneconfiguration, a coordinating DSA-enabled device may coordinate anddirect communication between DSA-enabled devices in a DSA-enablednetwork or a portion of a DSA-enabled network. In general, acoordinating DSA-enabled device may be any suitable DSA-enabled devicethat provides centralized control and/or coordination within theDSA-enabled network, including a base station, cell site, master device,access point, beacon device, coordinating node, or other suitabledevice. A coordinating DSA-enabled device may have a particular role orroles within a DSA-enabled network, in which a subset of all control orcoordination for the network is performed. For example, the coordinatingdevice may forward messages between devices, networks, and/or clusters;route messages among devices, networks, and/or clusters; providepolicies to other devices; perform some or all of the channel managementfunctions for one or more DSA-enabled networks; provide instructions orinformation to other devices regarding channel switching; manage one ormore detectors; provide gap and other timing and scheduling informationto other devices; provide software updates to other devices; analyze orrecord network topologies for DSA-enabled networks in a geographicregion; and any combination thereof and of other management functions.The various roles and functionality may be distributed among multipledevices in a DSA-enabled network, i.e., each function associated with acoordinating DSA-enabled device need not be performed by a single devicein the network. It will be understood by one of skill in the art thatany appropriate coordinating DSA-enabled device may be used, althoughthe present description may describe example embodiments using aparticular term or example coordinating device, such as where an examplenetwork is described in terms of a base station and/or subscriberDSA-enabled devices or units. A configuration having a base station orother coordinating DSA-enabled device may be referred to as aninfrastructure network. The non-coordinating DSA-enabled devices maycommunicate directly only with the base station, in which case the basestation may relay communication between the other DSA-enabled devices. Anon-coordinating DSA-enabled device also may be referred to as asubscriber DSA-enabled device, subscriber unit (SU), handset, portableunit, customer premises equipment (CPE), mobile station, slave device,user DSA-enabled device, end-user DSA-enabled device, peer, cellulartelephone, consumer device, cognitive radio, software defined radio, orscanner device. In another configuration, the base station may manage ordirect communication within a DSA-enabled network and subscriber unitsmay communicate directly with other subscriber units and with the basestation.

In another configuration, the DSA network may not use a base station orother specially-designated DSA-enabled device to manage communicationsamong DSA-enabled devices in a DSA-enabled network. Such a network maybe referred to as an ad-hoc network. In an ad-hoc network, a subscriberunit may be designated or elected as a temporary “lead DSA-enableddevice,” which may perform some or all of the functions typicallyperformed by a base station in an infrastructure network. The leadDSA-enabled device may be designated or elected temporarily, and thespecific DSA-enabled device performing one or more functions of a “leadDSA-enabled device” may change over time, such as where a new leadDSA-enabled device is chosen or designated each time a control functionis to be performed, or when a “lead DSA-enabled device” moves orotherwise becomes unreachable. In another configuration, no leadDSA-enabled device is designated, and communication among theDSA-enabled devices in the network is managed by way of control messagesbetween the network DSA-enabled devices.

FIGS. 4A-C show schematic representations of three example network typesaccording to embodiments of the invention. In FIGS. 4A and 4B, one ormore subscriber units (SUs) communicate with a base station (BS). Insome embodiments, such as the narrowband push-to-talk-implementationdescribed herein and other DSA network configurations, the BS andrelated functions may be referred to as a “beacon” or “master” and theSU may be referred to as a “scanner” or “user”. The base station maymanage or direct communication between and among the subscriber units.In FIG. 4A, the base station may manage communication in the DSA-enablednetwork while allowing subscriber units to communicate directly withother subscriber units. In FIG. 4B, the base station may manage everycommunication channel, so that a communication from one subscriber unitto another will pass through or be forwarded by the base station. Thetopologies illustrated in FIGS. 4A-B may be referred to asinfrastructure topologies due to the use of a base station or otherspecialized DSA-enabled device that manages communication within aDSA-enabled network.

FIG. 4C shows a peer-to-peer network containing only subscriber units(SUs). Such a network may be referred to as an ad-hoc network; in anad-hoc or similar network the subscriber units may be referred to as“peers” due to the lack of a base station or otherpermanently-designated controlling DSA-enabled device. In an ad-hocDSA-enabled network, one or more of the DSA-enabled devices maytemporarily perform some or all of the functions that would be performedby a base station in an infrastructure-type DSA-enabled network. Thesame DSA-enabled device may perform base station functions each time amanagement function is required, or a new DSA-enabled device may beselected or elected each time a base station function is required. Inanother example embodiment, a DSA-enabled device may assume one or morefunctions of a base station, and provide these functions to aDSA-enabled network for a period of time, and may subsequentlyrelinquish these functions at some future time.

In some embodiments, a base station may have the same or similarconfiguration as a subscriber unit. Such a DSA-enabled device may beconfigured to perform as either a base station or a subscriber unit, orit may be configured to perform as a base station on a first DSA-enablednetwork and as a subscriber unit on a second DSA-enabled network. Insome embodiments, a subscriber unit may temporarily or permanentlyassume the functions of a base station.

One potential limitation of some DSA-enabled and other radio systems isthat they may be unable to maintain connections with more than oneDSA-enabled network at a time. As DSA-enabled networks become morecommon, this limitation may undesirably limit the usefulness of aDSA-enabled device. In some embodiments of the invention, a DSA-enableddevice may be capable of operating in multiple DSA-enabled networksconcurrently.

FIG. 4D shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.In the example shown, a DSA-enabled device 400 has initiatedcommunication with (“rendezvoused with”) two DSA-enabled networks 401,402, and may send and receive information as part of each network.Specifically, DSA-enabled device 400 can operate as a DSA-enabled deviceon DSA-enabled network 401 (including participation as a base station,controlling DSA-enabled device, or other role), and can sense on behalfof DSA-enabled network 401, change channels, and perform other aspectsof being joined to DSA-enabled network 401. Concurrently, theDSA-enabled device 400 can operate as a DSA-enabled device onDSA-enabled network 402 (including operating as a subscriber device (asshown in diagram), as a base station, as a controlling DSA-enableddevice, or in any other permitted role), and can sense on behalf of theDSA-enabled network 402, change channels, and perform other aspects ofbeing joined to DSA-enabled network 402. In some cases, the DSA-enableddevice 400 may perform different roles in each DSA-enabled network towhich it is joined. This capability may be advantageous in severaloperating modes. For example, a DSA-enabled device user may be permittedto use a plurality of DSA-enabled networks, such as when there aremultiple DSA-enabled networks established for a geographic region. Auser who is permitted to receive information from both a firstDSA-enabled network, and a second DSA-enabled network concurrently canreceive information from the first DSA-enabled network while using thesecond DSA-enabled network, on the same DSA-enabled device. As aspecific example, the first DSA-enabled network may be a digital contentbroadcast network (a DSA-enabled network that provides content, such asa 802.22-based network that supports digital TV broadcasts), and thesecond network may be a DSA-enabled digital content broadcast network, aDSA-enabled communications network, a DSA-enabled public safety network,or another type of DSA-enabled network.

As another example, the ability to concurrently operate in a pluralityof DSA-enabled networks may be used when a DSA-enabled device is mobileand is travelling among DSA-enabled networks, and it may join a firstDSA-enabled network and subsequently join one or more additionalDSA-enabled networks as they become available. Transmission traffic maybe routed to the DSA-enabled network that provides connectivity to theoriginating DSA-enabled device, the nearest DSA-enabled device, theDSA-enabled device with the strongest signal, the DSA-enabled devicewith the best connectivity, or combinations thereof.

FIG. 4E shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.In this configuration, a DSA-enabled device 420 has rendezvoused withtwo DSA-enabled networks 403, 404, and may send and receive informationas part of each network. Specifically, the DSA-enabled device 420 canoperate as a DSA-enabled device on DSA-enabled network 403 and can senseon behalf of DSA-enabled network 403, change channels, and perform otheraspects of being joined to DSA-enabled network 403. Similarly,DSA-enabled device 420 may operate as a DSA-enabled device on anotherDSA-enabled network 404 as a controlling DSA-enabled device for thenetwork 404, and can sense on behalf of DSA-enabled network 404, changechannels, and perform other aspects of being joined to the secondDSA-enabled network 404. The DSA-enabled device 420 may route networkpackets between the DSA-enabled networks 403 and 404 in accordance withpolicies established for either or both DSA-enabled networks 403 and404. For example, a single network operator may establish a plurality ofnetworks, and allow users to “roam,” i.e., move between the networksusing mobile DSA-enabled devices. Such a configuration may be used, forexample, when it is desirable not to incur delays associated withre-establishing connections to alternate networks as the DSA-enableddevice moves in and out of range of base stations on the networks. Forexample, when a voice conversation is transmitted between theDSA-enabled device 420 and a recipient operating in either of theDSA-enabled networks, or in an external network (not shown), the latencycaused by re-connecting to a new network each time a mobile DSA-enableddevice moves between a plurality of DSA-enabled networks may causeunacceptable delays to the voice traffic. A DSA-enabled device mayreduce or eliminate this limitation by supporting multiple networks asdescribed. As illustrated in FIG. 4E, the DSA-enabled networks 403, 404may each be an infrastructure network. However, it will be understood byone of skill in the art that this is provided merely as an example, andany other network structures and topologies may be used. Further, theDSA-enabled device may perform any role or function within each of thenetworks 403, 404, such as base station, subscriber unit, or other role.

FIG. 4F shows an example of a DSA-enabled device operating concurrentlyin two DSA-enabled networks according to an embodiment of the invention.A DSA-enabled device 430 may operate concurrently in two DSA-enablednetworks 405, 406 using a plurality of transceivers 432, 434. In thisconfiguration, the DSA-enabled device 430 has rendezvoused with bothDSA-enabled networks 405, 406 and may send and receive information aspart of each network. Specifically, DSA-enabled device 430 may operateas a DSA-enabled device on DSA-enabled network 405 and can sense onbehalf of DSA-enabled network 405, change channels, and perform otheraspects of being joined to the DSA-enabled network 405. Similarly, theDSA-enabled device 430 may operate as a DSA-enabled device onDSA-enabled network 406 as a controlling DSA-enabled device and cansense on behalf of DSA-enabled network 406, change channels, and performother aspects of being joined to DSA-enabled network 406. TheDSA-enabled device 430 may operate in any role (e.g. base station,subscriber unit) within each of the networks, and may have differingroles in different networks 405, 406. As a specific example, FIG. 4Fshows a configuration in which the DSA-enabled device 430 uses a firsttransceiver 432 to operate as a subscriber node in a first DSA-enablednetwork 405, and a second transceiver 434 to operate as a base stationin a second DSA-enabled network 406. In addition, the DSA-enabled device430 may route network packets between DSA-enabled networks 405 and 406in accordance with policies established for either or both DSA-enablednetworks 405 and/or 406. For example, a plurality of network operatorsmay establish a plurality of networks, and a particular DSA-enableddevice may operate on both networks and pass traffic between thenetworks. A multi-transceiver configuration as illustrated in FIG. 4Falso may be used when multiple DSA-enabled networks 405 and/or 406 havehigh utilization, are not synchronized (e.g. they have different framingand/or gap rates), or use substantially different channels. Amulti-transceiver DSA-enabled device may partially or entirely mitigateundesirable effects arising from such situations and configurations.

Each of the example networks illustrated in FIGS. 4A-4F may be a portionof a larger network. For example, each illustrated network may be a cellor cluster in a cellular network or other similar network topology.

Unless stated otherwise, the methods, devices, and systems describedherein may operate in any network topology. In general, a DSA-enableddevice as described herein may be a base station, a subscriber unit, oran ad-hoc DSA-enabled device that may function as a base station and/ora subscriber unit. For example, although some functionality is describedas performed by a base station, it will be understood that similaroperations and processes may be performed by, for example, a leadDSA-enabled device or temporary lead DSA-enabled device in an ad-hocsystem, or may be distributed among subscriber units in an ad-hocsystem.

DSA systems according to embodiments of the present invention mayperform communication and spectrum scanning and analysis functions asdescribed herein without noticeable or appreciable interruption to thecommunications between cooperative DSA-enabled devices. To do so,various scheduling and resource management techniques may be used. Forexample, spectrum sensing/detection may be performed at a ratesufficient to detect a non-cooperative signal and prevent or reduceinterference with the non-cooperative system, but at a low enough rateto avoid noticeable interruption of communication with other cooperativeDSA-enabled devices. For example, within a given time frame,communication times and spectrum sensing times may be interleaved intime slots sufficiently small to prevent communication from beingnoticeably interrupted, but large enough for spectrum sensing to beeffective at finding other signals. In an embodiment, about 10% ofresources may be allocated to sensing functions. For example, about 10%of any given time frame may be used to perform spectrum sensing. Asdescribed in further detail below, this time may be scheduled to performdifferent amount or degree of spectrum sensing for different channels,such as where high-priority channels receive a greater share of thesensing time. As another example, each frame may include a sensingperiod that represents a relatively small portion of the frame, such aswhere a sensing period of about 0.5 ms is scheduled within a 20 msframe. In some embodiments, concurrent sensing and communication methodsmay allow for specific hardware configurations, or make certain hardwareconfigurations more efficient. For example, in an embodiment aDSA-enabled device may communicate and monitor spectrum usageconcurrently using a single antenna, though in general multiple antennasalso may be used. In some embodiments, the concurrent sensing andcommunication techniques described herein may allow a single-antennadevice to operate more efficiently than would be possible using asimplistic scheduling technique.

In some embodiments, spectrum monitoring may be performed on channelsthat are in use by the DSA-enabled device, channels that may beavailable for use but not currently used, channels that are notavailable for use, or various combinations thereof. Monitoring channelsother than those in use may allow a DSA-enabled device or network tomore rapidly switch channels than would otherwise be possible, as wellas reducing or eliminating the need to perform additional scanning oncea channel switch takes place. Multiple detectors may be used and, insome embodiments, different detectors are applied to specific frequencybands so as to improve sensitivity or performance of the DSA-enableddevice or network. In some embodiments, a DSA-enabled device may performdetection and communication using a single antenna. Embodiments of thepresent invention may allow a DSA-enabled device to communicate and toperform sensing in the same region of spectrum and, more specifically,on the spectrum specified as part of a channel or set of channels. Thus,it will be understood by one of skill in the art that when a DSA-enableddevice or network is described herein as communicating on a channel, theDSA-enabled device or network also may perform environmental sensing ofthe same channel using the techniques described herein.

Sensing regions of spectrum that include channels other than thosechannels currently in use by a DSA-enabled device or network may reducethe delay involved in moving to another channel once a non-cooperativesignal is detected in a channel being used by a DSA-enabled network byreducing or avoiding additional delay involved in scanning otherchannels. Also, with some applications a non-occupancy time period(i.e., the time the system must wait before using a channel after aprimary signal has been detected in it) may be relatively high, forexample up to 30 minutes. By sensing on numerous channels, theDSA-enabled device may know of several candidate backup channels shouldthe channel need to be changed and one of the backup channels is foundto be unavailable for the non-occupancy time period. It also may be moreconvenient and/or straightforward to sense on all channels within aparticular region of spectrum rather than to decide on a subset ofchannels to scan prior to sensing.

FIGS. 5 and 6 show example system flow diagrams for a DSA-enabled deviceperforming a concurrent scanning and communication process according toembodiments of the invention. One or more detectors 112 may beconfigured to detect cooperative and/or non-cooperative signals in oneor more channels. Multiple detectors may be used, even where a singlechannel or a group of channels is being detected. For example, wirelessmicrophones operate in the TV region of the radio spectrum; thus, whendetecting in the TV bands both wireless microphone and TV detectors maybe used. Other detectors and combinations of detectors as describedherein may be used. Further details regarding the use of detectors in aDSA system and specific examples of suitable detectors are provided infurther detail below.

The portions of spectrum available for use and actually used by aDSA-enabled device or network may be defined by a combination of thespectrum selected by an operator of the device or network, the spectrumin which the DSA-enabled devices are capable of operating, and accesslimitations set by policy, regulatory, service provider, and otherrequirements. FIG. 7 is a specific example showing how various regionsof spectrum may be utilized by a DSA-enabled network in an embodiment ofthe invention. At the top, various spectrum regions and definitions areidentified. One or more spectrum bands 840, such as bands licensed forspecific use by a regulatory agency, may define regions of the spectrum.A spectrum plan 841 may be pre-defined for a DSA-enabled device or aDSA-enabled network, which restricts the DSA-enabled device and/or theDSA-enabled network to using certain regions of the spectrum. A spectrumplan or frequency plan may define one or more channels for a particularDSA-enabled network. The spectrum plan may operate as a constraint onDSA operation, similar to a set of policy rules, which define the set ofchannels to be used by the DSA-enabled network. The example shown inFIG. 8 shows a spectrum plan that omits the cellular band and portionsof unlicensed, radar, and government (DoD) bands from consideration foruse by the DSA system. A DSA-enabled device also may have a particularcapability range 842 that determines what portions of spectrum theDSA-enabled device is physically able to use. For example, certainspectrum ranges may be omitted from design of a DSA-enabled device dueto power or processing considerations, regulatory requirements, physicalantenna limitations, or other reasons. Thus, the total accessiblespectrum 844 may be defined by the spectrum plan 841, the DSA-enableddevice or system capability 842, and policy requirements. Scanning anddetector requirements 845, 846, respectively, may describe the detectorsused by the DSA-enabled device and various metrics applied across theaccessible spectrum 844. The requirements 845, 846 may be provided asinput to a scheduler or other component of a DSA-enabled device.

In an embodiment, the detectors 112 may operate primarily or only onaccessible regions of the spectrum. A DSA-enabled device may sense itsRF environment based on the regulatory bands 840 in which sensingoccurs, the devices expected to be operating in each band, and thecapabilities and configuration of the DSA-enabled device. Examples ofband-specific sensing requirements and detector requirements are shownin FIG. 9. However, it will be understood that other requirements andconfigurations may be used. The regions of spectrum corresponding toeach set of requirements are labeled with corresponding letters (A, B,C, D, F) in FIGS. 7-10.

Various techniques may be used to distribute the spectrum scanning load(i.e., to distribute the scheduled sensing times among variouschannels). In an embodiment, a bounded, greedy algorithm, in which alocally-optimal choice, i.e., a choice made at each step of theallocation process that is optimal or believed optimal at that step, isused to reduce or minimize the demand on device resources and increasecommunications. This may satisfy band-specific sensing requirements at aminimum “cost” in terms of communication resource utilization and deviceprocessing load. As described in further detail herein, a detectorscheduler (i.e., a “high-level scheduler”) may arrange sensing schedulesby sensing a particular portion of spectrum using specific detectors.For example, the scheduler may attempt to optimize the schedule based onthe sensing requirements, such as the scan rate specified for thatportion of the spectrum, and/or using only specific detectors configuredfor that portion of spectrum, or detectors that are particularly suitedfor the given region. Notably, the scheduler and detectors may use adifferent channelization than the transceiver such as the radio 150described with respect to FIGS. 1A and B, that is used by theDSA-enabled device. For example, for ease of use a radio in aDSA-enabled device may communicate at previously-defined channels interms of regulatory bands. However, the DSA-enabled device may detectand evaluate spectrum using a channelization designed to improveefficiency and/or increase the chance of detecting a non-cooperativetransmission. The channelization suitable for detection and evaluationmay not match the channelization used to communicate with otherDSA-enabled devices. For example, in some embodiments one or moredetectors may use channelizations that differ from those used by otherparts of a DSA-enabled device or system, such as the logical channeltable and use tables described in further detail below.

Band-specific sensing requirements may be used to prevent or reduce thechance of interference with non-cooperative, non-DSA signals or devices,and/or non-cooperative DSA signals or devices, and to enable discoveryof and connection with cooperative DSA-enabled devices. For example,different bands may have different technical or regulatory requirements,and there may be little or no benefit to using more stringent orburdensome sensing requirements.

Band-specific detector requirements may be derived from the sensingrequirements and the detection capabilities of the DSA-enabled device.Detector requirements may be translated into detector configurationswhich specify detector type and type-specific parameters. For example,FIGS. 7-9 refer to four detector types (wideband, TV, wirelessmicrophone and radar) and five detector configurations (including twodifferent wideband types). Detector configurations may be derived fromthe detector requirements to efficiently distribute communicationresource utilization and processing load. The accessible spectrum,sensing and detector requirements may be determined prior to initiationof a DSA-enabled device or system, or during operation of the DSAsystem. Examples of specific detectors and detector configurations aredescribed in further detail below.

Referring again to FIGS. 5-6, the detectors 112 may provide raw dataincluding the latest results of sensing in one or more channels and scanhistory data to one or more classifiers 134. In some embodiments, eachdetector is associated with a classifier using a classificationalgorithm tailored to or otherwise particularly suited to its associateddetector type. The latest scan results and a scan history may beprovided to the classifiers.

After the classifiers 134 process the raw data, classification resultsand channel decisions may be provided to a policy module 140, channelmanager 132, or other modules in the DSA-enabled device as describedherein. Information from the classifiers and the policy module may beused by a channel manager 132 to generate channel rankings that specifypreferred channels for use or scanning by the DSA system. In anembodiment, the channel manager 132 maintains spectrum data in a LogicalChannel Table (LCT). The LCT may include only information regardingspectrum that is potentially-accessible to the DSA system, includingsensing and detector requirements. Such a configuration may prevent orreduce use of detection resources on inaccessible or undesirable regionsof the spectrum. An LCT may represent spectrum in Logical Channel Units(LCUs), which quantize available spectrum into logical channels. Asmaller LCU (i.e., encompassing less spectrum) may allow for greaterpotential spectrum utilization, but also may require additionaldetection and processing resources relative to a larger LCU.

The various outputs described with respect to FIG. 5 may be stored inone or more computer readable storage mechanisms, such as data tablesstored in the memory of a general purpose processor. In someembodiments, historical data also may be retained. For example,detection results may be stored in a data store for various amounts oftime depending on the specific channels associated with the results. Theclassifier 134 also may use historical detection data to classifysignals detected by the detectors. Examples of using historical data,such as with Group Behavior techniques, are described herein and in U.S.patent application Ser. No. 11/432,536, filed May 12, 2006 and publishedas U.S. Pub. No. 2007/0263566 on Nov. 15, 2007, the disclosure of whichis incorporated by reference in its entirety.

The channel manager may use various techniques to store and manage datain the LCT. In an embodiment, LCUs may be defined based on detectorcharacteristics, detector availability, and spectrum requirements. Thechannel manager may then assign each LCU to a use category, such as byplacing the LCU in a virtual use table. The use tables are then used bythe DSA system to discriminate between channels based on channelpriority and preference. In an embodiment, the use tables may categorizeLCUs as active, backup, candidate, and possible. Active channels arethose that are currently in use for communication by a DSA-enableddevice. Backup channels represent spectrum that can be used if itbecomes necessary for the DSA-enabled device to stop use of one or moreactive channels and move to a different region of the spectrum. If theamount of spectrum accessible to the DSA-enabled device is relativelylarge, the DSA-enabled device may assess a subset of the spectrum forpotential inclusion as backup channels. Candidate channels are thosewhere cooperative DSA signals have been detected. These channels may beused by a communication coordinator (rendezvous) module to establish andmaintain communication with other cooperative DSA-enabled devices.Possible channels refer to spectrum that is accessible by theDSA-enabled device. As previously indicated, a subset of the accessiblespectrum may be designated as “possible” when the accessible spectrum isrelatively large. Further details regarding operation of a scheduler andspecific examples of scheduling processes are provided in further detailbelow. Different priorities may be assigned to different use tables, andthe channels listed in each use table may be managed differently by aDSA-enabled device or network. For example, a scheduler may directadditional or higher-fidelity detection at candidate channel spectrum toimprove and assist in the process of establishing and maintainingcommunication with other cooperative DSA-enabled devices. As anotherexample, spectrum sensing may be performed on backup channels more oftenthan on other channels to increase the chance that a usable backupchannel is available when needed, which may result in the backup channellist being of a higher fidelity than if the entire range of accessiblespectrum was monitored equally. As another example, active channels maybe verified as being available for use by the DSA-enabled network morefrequently than backup, candidate, and/or possible channels, to reducethe likelihood of creating interference with a non-cooperative device.

Different detection requirements also may be applied to each use table.For example, co-channel sensing requirements may be applied to activeand backup channels. Co-channel sensing requirements cause theDSA-enabled device to examine channels or regions of spectrum expectedto have a high likelihood of interference from the relevant channelsmore closely. Examples of such regions of spectrum include channels thatare harmonics of a channel used by the device, cross-products of achannel used by a device and an expected non-cooperative channel, andpredefined offsets of a channel used by a device. DSA detectionrequirements, in which the DSA-enabled device examines the relevantspectrum for use by other cooperative or non-cooperative DSA-enableddevices, may be applied to candidate channels. For possible channels,“best effort” requirements may be applied, in which the DSA-enableddevice makes a best reasonable attempt to include these channels in itsspectrum monitoring schedule.

FIG. 8 shows an example set of use tables as channels are assignedduring a span of time. The regulatory bands 840, spectrum plan 841,DSA-enabled device capability 842, DSA accessible spectrum 843, sensingrequirements 834, and detector requirements 845 as shown in FIG. 7 arereproduced at the top of the spectrum chart for reference. It will beunderstood that the specific arrangement of spectrum classification, DSAcapability, sensing and detector requirements, and LCU arrangement isprovided as an example, and other configurations may be used. Aspreviously indicated, spectrum may be divided into logical channel units(LCUs) 850 that are assigned to various categories within the LCT. TheLCUs 850 illustrated in FIG. 8 are provided as examples only. The LCUsand other regions of spectrum are not necessarily shown to scalerelative to the other portions of the spectrum, such as the bands 840.

At a time T0, all channels in the LCT may be assigned as possiblechannels, i.e., listed in the possible channel use table. TheDSA-enabled device may perform spectrum sensing and detection duringthis period. At a later time T1, channels in two regions of spectrum851, 852 are assigned as candidate channels. Each region may include oneor more channels, although channels assigned to a particular categoryneed not be adjacent or otherwise in the same region of spectrum. At alater time T2, one or more of the previously candidate channels 852 areassigned as active channels, indicating that the DSA-enabled device isusing them for communicating with other cooperative DSA-enabled devices.Other channels 853 are assigned as backup channels, and additionalcandidate channels 854 may be identified. A previous candidate channel851 may be un-assigned, so that it is no longer assigned as a candidatechannel. For example, a channel may be un-assigned because a previousclassification expires (i.e., a set time for which the classificationwas to be considered valid or appropriate expired) the classificationotherwise becomes no longer valid, because the DSA network is not ableto perform a rendezvous process on the channel, or for other reasons. Asshown, various other channels may be assigned as active, backup,candidate, and possible channels at subsequent times T3, T4.

In some embodiments, a single channel may be sensed by multipledetectors or multiple configurations of a single detector. For example,the second candidate channel 852 assigned at time T1 can be sensed bytwo detectors (WB-1 and WB-2) instead of only one detector (WB-1)available for the first channel 851. The example detectors WB-1 and WB-2may be separate physical detectors, or they may represent differentconfigurations or operating modes of a single physical detector.Multiple detectors may be used to sense a single channel, for example,when sensing requirements demand better sensitivity than is availablewith a single detector. As a specific example, a first detector WB-1 maybe used for initial DSA detection while performing an initial rendezvousprocess. A second detector WB-2 may be configured with a smallerresolution bandwidth, and used to detect non-cooperative signals. Asanother example, multiple detectors may be used when a region ofspectrum may be used by different types of devices and/or for differentuses, such as where the TV spectrum is used for both televisionbroadcast and wireless microphone operation. In such a configuration, adifferent detector may be used for each expected use of spectrumcorresponding to channels sensed by the detectors. In general, sensingrequirements may imply or require the use of different detectors withindifferent regions of the spectrum and/or with different expected typesof non-cooperative spectrum usage.

Referring again to FIGS. 5-6, the channel list may be used by ascheduler 122 to manage operation of the detectors 112 to scan channelsthat may be suitable for use by the DSA system. FIG. 10 shows a specificexample of using different channel categories during an arbitrary windowof time between T3 and T4 in FIG. 8 to schedule detector operationsaccording to an embodiment of the invention. The sensing and detectorrequirements as shown in FIGS. 7-8 are reproduced at the top of FIG. 10for reference. Different sensing schemes may be used based on howspectrum is categorized in the LCT, and may result in various scanningtechniques appropriate for specific portions of the spectrum. Scanningtechniques may vary the scanning interval (the time between successiveobservations by a detector), the scanning frequency (the frequenciessensed in a region of spectrum), the frequency interval (how often aspectrum frequency range is scanned), the type and number of detectorsused, and other variables related to scanning. For example, active(in-use) channels may be scanned as required to meet sensingrequirements listed in the LCT. Spectrum associated with backup channelsalso may be scanned (i.e., these channels may be sensed with a detector)in accordance with the requirements in the LCT, but the sensing may belimited in embodiments by sensing allocation and processing capacityconstraints. Finally, possible channel spectrum may be scanned on a“best efforts” basis as determined by the availability of sensingresources after higher priority sensing is accomplished as well asprocessing capacity. As a specific example, the active channel(s) 861may be scanned using a wideband detector (e.g., WB-1) at a relativelyhigh scanning interval, such as every 100 ms. The backup channels 862,863, 864, and 865 may be scanned at a lower interval, e.g., every 200 msusing the WB-1 detector. In some embodiments, different channels of thesame LCT category may have additional or different scanningrequirements. For example, a backup channel 864 also may be scannedusing an additional detector, such as the TV detector TV-1, at adifferent scanning interval, e.g., every 1800 ms. The possible channelsmay be scanned at the best rate available after other scanningrequirements are met using band-appropriate detectors. For example, thechannels may be scanned using a frequency interval of about 0.01 Hzusing an appropriate detector. Other combinations and scanningrequirements may be used.

In an embodiment, the scheduler may generate detection schedules thatsimultaneously or concurrently support multiple detection rates acrossone or more detector paths and/or multiple detector configurations.Detector schedules may be configured to reduce or minimize detection“costs” while satisfying sensing requirements. For example, TV-banddetectors typically are more “costly” in terms of the time required forscanning. In an embodiment, such detectors may be used only for sensingin particular time segments, such as the spectrum time segment labeled864 in FIG. 10. The sensing time may be set at low as allowed by policymanagement, technical, and regulatory considerations. For example, aregulatory scheme may require a TV detector to sense every 1800 secondsfor 30 seconds. In the example, if a TV is detected in band 864, thenext scan may be determined by a Non-Occupancy Time period, whichspecifies the time during which a band is considered off-limits for theDSA system following detection of the TV signal. As a specific example,a Non-Occupancy Time period may range from about 1 second for widebandsignals to about 30 minutes for radar signals. Thus, the schedulertypically is configured to avoid unnecessary scanning.

In an embodiment, all accessible channels are listed as possiblechannels. In addition, LCUs may be listed in other tables, such as abackup channel table. The use tables may be modified whennon-cooperative signals are identified. For example, if anon-cooperative signal is identified on a backup channel, the channelmay be removed from the use table. FIG. 11 shows an example of use howtables may be modified after time T4, when one or more non-cooperative(NC) signals are detected in two portions 871, 872 of the spectrum beingmonitored. FIGS. 12 and 13 show corresponding data flows within aDSA-enabled device according to embodiments of the invention. When an NCsignal is detected, such as in channel regions 864 and a portion of 865,a corresponding LCU may be removed from the backup LCT but remain in thepossible table. The channels may be reclassified by the channel manager,which may receive direction from a policy module. For example, some ofthe channels in region 865 may be removed from the backup channel table,resulting in fewer channels in the region 865′ being classified asbackup channels. The channel manager also may compensate for thereduction in backup spectrum, for example, by adding additional channelsto the backup table. In the example shown in FIG. 11, for example, onebackup interval 862 is expanded to include additional channels 862′(i.e., additional channels are classified as backup channels) and newchannel 876, 877 are classified as backup channels. The scheduler maythen generate a subsequent detector schedule based on the updated usetables and the sensing/detector requirements. When an LCU becomesnon-accessible, such as due to a policy requirement, it may be removedfrom all use tables.

FIG. 14 shows an example of sensing time period allocation as may beperformed by a scheduler according to an embodiment of the invention.The configurable parameter t_(guard) _(—) _(time) defines the timeoffset reserved between the start of executing a detector work list andthe execution of the first measurement of spectrum from the activechannel table. This offset may mitigate time uncertainty associated withsynchronization of sensing allocations among cooperative DSA-enableddevices in a particular DSA network. To more efficiently use detectiontime during sensing allocations, the first spectrum measurements may beperformed over channels from the possible table since possible channelstypically are unaffected by synchronization uncertainty. The multipledetections may be performed during a single sensing allocation time(i.e., during a single gap). Allocation time uncertainty caused byimperfect time synchronization among a networks DSA-enabled devices mayresult in some DSA-enabled devices still transmitting during a portionof the time that others have already begun detecting on active channels.To avoid or reduce resulting problems, detections may be shifted overactive channels so as to begin slightly after the beginning of thecoordinated gap period. To use sensing time efficiently, sensing may beperformed over possible channels at the beginning of the gap period—any“leftover” transmissions made by DSA-enabled devices that slightly lagthe beginning of the gap period will be on different channels, and thushave less or no negative effect on the sensing of possible channels. Ingeneral the empty time period 3910 may be present in, for example,situations in which an additional measurement may not be performedwithin a sensing time period allocation (i.e., the empty duration 3910is less than the time required to perform another measurement), or inwhich all the possible spectrum, or all spectrum of interest, has beensensed in less than a full sensing time period allocation.

Two types of sensing allocation may be used, including coordinatedsensing allocation such as, for example, the sensing methods describedherein with reference to distributed detection and group behavior, andlocal sensing allocation. As previously described, during coordinatedsensing DSA-enabled devices may refrain from transmitting to allow fordetection of non-cooperative signals on channels being used by aDSA-enabled network. In contrast, with a local sensing allocationscheme, neighbor DSA-enabled devices may not be required to ceasetransmission during the scan period. An individual DSA-enabled devicemay perform local sensing to enhance spectrum usage without causinginterference with others. Local sensing allocation may be used fordiscovering existing DSA channels.

Work lists generated by the scheduler may outline detection events to beperformed by one or more detectors during the allocated sensing time. Asused herein, a “detection event” refers to an instruction to detect atone or more specified frequencies for a specified period of time, usingone or more specified detectors. Upon completion of a work list, thescheduler 122 may send it to the media access control (MAC) which inturn forwards it to the physical layer or related API of an appropriatedetector 112. The scheduler may coordinate detection to prevent thedetector and the detector results processor from becoming overloaded.Various parameters may be specified for a detection event, such asfrequency at which to detect, gain value, number of samples to becollected, detector type to use, configuration profile of the detector,output data format requested, whether to return the accumulated output(a.k.a. results fragment) via callback after completion of the detectionevent, length of the detection event output in samples, number ofdetection events in the work list, or any combination thereof. Thedetector type and configuration profile of the detector for each eventmay be computed based on the detection objective (e.g., neighbordiscovery vs. non-cooperative detection) and sensing requirementsreceived from the policy manager.

In some embodiments, the scheduler may perform several functions:request and management of sensing allocations, generation of detectorwork lists, and control of detection pace. FIGS. 15A and 15B show anexample message sequence diagram showing the interaction between ascheduler and other DSA components according to such an embodiment ofthe invention. For clarity, the diagram shows each portion of detectorresults returned in a single message. However, it will be understoodthat detection results could be received in multiple fragments. Inaddition, various instructions and requests may include a correspondingacknowledgement message which is not shown. For example, in response toa detect instruction sent from the scheduler 122 to the MAC 4015, theMAC may return a detect acknowledgement. In general, the scheduler 122may generate two main items: sensor allocation (s-allocation) requestsand work lists. A sensor allocation may include the followingparameters: allocation ID, allocation period, size of sensingallocation, effective duration of sensing allocation, number oftransceivers per allocation, and allocation type. Depending onrequirements and the state of the entire system, a request can be sentto obtain a new sensor allocation, update an existing allocation, orrelease an existing allocation. Although FIGS. 15A-B show communicationwith the detector(s) 112, it will be understood that a series ofcommunications related to a particular detection event referring to asingle detector.

The scheduling process may begin when a channel manager 132 or otherelement of a DSA-enabled device sends a schedule request 4021 to thescheduler 122. The scheduler may then generate a sensor allocation at4022, and send an allocation request or instruction 4023 to the MAC. TheMAC may generate a sensor allocation at 4024 and send an acknowledgementto the scheduler at 4025.

The scheduler may generate a first work list (WL 1) at 4026, whichspecifies behavior for one or more detectors associated with theschedule received by the scheduler 4021. A detect instruction for thefirst work list is sent to the MAC at 4027 and, similarly, the MACinstructs one or more detectors 4028 to perform the appropriatedetection 4029. After the detection is complete, the detector(s) senddetection results 4030 to the MAC, which may forward results at 4031 toanother component, such as a detector results processor 4010. In anembodiment, the detector results processor 4010 may be or may implementa signal classifier or signal classifier functions as previouslydescribed, such as the signal classifier 134 described with respect toFIG. 1A. The detector results processor processes the detection resultsat 4032 and notifies the scheduler when processing is completed at 4033.The analysis generated by the results processor 4010 may be sent toother DSA components, such as a channel manager.

The scheduler may generate a second work list (WL 2) at 4040. Notably,the work list may be generated prior to receiving an indication thatdetection scheduled by the first work list is complete. Detect commands4041, 4042 are sent to the appropriate detector(s) as previouslydescribed with respect to WL 1, and the detector(s) perform detection4043 as directed. In some cases, the scheduler may issue an abortcommand 4051, such as where detection is taking a longer time thanexpected or defined by the work list, or where the DSA-enabled deviceindicates a need to halt detection. The abort command may beacknowledged by the detector via appropriate messages 4053, 4054, 4055to the MAC, detector results processor, and/or scheduler. In someembodiments, partial or full results may be returned by the detector(s)after detection is aborted. The results may be analyzed by the detectorresults processor, or they may be discarded.

In some cases a particular work list may not be performed. For example,in FIGS. 15A-B Work List 2 (WL 2) takes a longer time to perform thaninitially defined by the scheduler, as identified by the “timeout”period 4050 associated with WL 2. This may cause the scheduler to skipgeneration of the next Work List (e.g., WL 3), and continue to the nextwith Work List 4 (WL4). The scheduler also may send an abort command4051 to stop associated scanning as previously described. The subsequentwork list WL 4 may then be processed and associated detection performedas previously described.

Additional details regarding the use of a scheduler in a DSA-enableddevice and system, the interaction of the scheduler with various otherhardware components of a DSA-enabled device, and specific examples ofscheduler hardware and software configurations are provided in furtherdetail below.

FIG. 16 shows an example of two DSA-enabled devices operating during atime span in which each DSA-enabled device has various detection periodsand transmission/reception periods. If one DSA-enabled device 501attempts to perform detection during a time period 510 in which a secondDSA-enabled device 502 is transmitting, the first DSA-enabled device 501may detect transmissions from the second DSA-enabled device 502 asnon-cooperative signals, which may then be mis-classified as originatingfrom a non-cooperative source. Additionally, a signal transmitted by thesecond DSA-enabled device 502 may hide the presence of signals from oneor more non-cooperative sources received by the first DSA-enabled device501.

To reduce or eliminate these effects, a detection gap, or quiet period,may be used. Detection times may be coordinated between all orsubstantially all DSA-enabled devices in a network. “Substantially all”DSA-enabled devices refers to those DSA-enabled devices that are in aproximity or geographic region defined, for example, by a communication,detection, or interference distance. Those DSA-enabled devices that areoutside of a communication, detection, or interference distance may notbe synchronized with the DSA-enabled devices within the same range, butthe lack of synchronization to out-of-range DSA-enabled devicestypically does not adversely affect the ability to detect and classifyreceived signals. Typically, the interference distance is the primarydistance of concern in synchronizing. In an embodiment, the detectiontimes may be coordinated between all DSA-enabled devices in a geographicregion, including DSA-enabled devices and networks that would beconsidered non-cooperative by the other DSA-enabled devices or networksin the region. This synchronization could be achieved using, forexample, a global positioning system (GPS) clock or othersynchronization techniques.

In an embodiment, the synchronization of a detection gap may occur onlybetween the DSA-enabled devices of a particular network. This can occurunder instruction, either from a base station and/or by an externalpolicy definition that defines the specific detection intervals. Inanother embodiment, the detection times may be coordinated between allDSA-enabled devices in a geographic region, across all DSA-enableddevices on a network, or across different DSA-enabled devices andnetworks, including DSA-enabled devices and networks that would beconsidered non-cooperative by the other DSA-enabled devices or networksin the region. In such an embodiment, DSA-enabled devices sharing acommon detection gap may synchronize their timing to a common clock anduse specific detection intervals. Policy definitions may be used todefine the specific detection intervals, the intervals may be determinedby the DSA-enabled devices based in part upon observations ofsurrounding spectrum usage, and/or the DSA-enabled devices can taketheir detection interval specifications from a common control channel.In general, time synchronization between DSA-enabled devices can occurat a MAC level or using a common broadcast time source, such as a GPSclock or a common clock control channel.

In an embodiment, all of the DSA-enabled devices within a region maycease transmissions for a synchronized time period, which may berelatively short and periodic. As a specific example, the synchronizedtime period may occur about 1-100 times a second, for times of about 1μs to about 100 ms. A detection time period synchronized amongDSA-enabled devices in a network or region may be referred to as a“detection gap”. The use of a detection gap also may be useful forrelatively closely-spaced DSA-enabled devices, particularly when devicesare within the interference distance of other devices, since detectionmay be blocked for DSA-enabled devices in close proximity to otherDSA-enabled devices as previously described. The detection gap may bescheduled to occur periodically, on a scheduled basis, according to ascheduling algorithm, pseudorandomly, and the like, or some combinationthereof.

Other embodiments may include various changes to the synchronized gaptiming, duration, or other characteristics. For example, the geographicbreadth may be varied to include more or fewer cooperative DSA-enableddevices. The synchronized gap may be implemented on the fly, or it mayoccur at pre-set times or locations within a frame. A synchronized gapmay be used with any structure of the network, e.g., infrastructurenetworks as well as with ad-hoc or peer-to-peer type networks.

FIG. 17 shows an example of two DSA-enabled devices that use a detectiongap according to embodiments of the present invention. As shown in FIG.17, the use of a detection gap may allow DSA-enabled devices to sensenon-cooperative signals with a relatively high sensitivity. The use ofthis first detection gap also may reduce or eliminate false alarmscaused by detection and incorrect characterization of other DSA signals,since DSA transmissions do not occur during the detection periods. Insome embodiments, a detection gap may be shared among all cooperativeDSA-enabled devices in a region or network. In other embodiments, adetection gap may be shared among all DSA-enabled devices in a region,even if they are in separate networks.

Coordination of the detection gap may be accomplished by a networking orMAC (media access control) protocol. For example, in a centralized orinfrastructure-type network, a base station may mandate a synchronizeddetection time to other DSA-enabled devices in the network. Aninfrastructure-type network also may include many central controllers,such as in a cellular configuration, in which case each centralcontroller may mandate the synchronized detection time for thoseDSA-enabled devices in its network. The synchronized detection time alsomay be synchronized among the multiple central controllers. In adistributed or ad-hoc system, a distributed detection time alignmentprotocol that operates without a central coordinator may be used. Such aprotocol may operate with relatively little global information, andwithout relying on previous assignments of roles to DSA-enabled devicesnor resource reservations. A specific example of a suitable distributedtime alignment protocol is the Hybrid Contention/TDMA-based (HCT) MACthat is designed to work with ad-hoc wireless networks organized inclusters, providing timely bounded communications both inside andoutside the clusters. An example of one such protocol is described inCeara Fortaleza, “A wireless hybrid contention/TDMA-based MAC forreal-time mobile application,” Symposium on Applied Computing,Proceedings of the 2008 ACM symposium on Applied computing. In thisexample protocol, to create a detection slot, each of the DSA-enableddevices sets aside a portion of each TDMA frame. Because a DSA systemmay use multiple channels, which may be non-contiguous within thespectrum, all DSA-enabled devices in a network or region may coordinatethe detection gap even if they operate on different frequencies.

In an embodiment, the synchronized detection period may be scheduled tooccur at different points within communication frames. For example, aDSA network may use a frame structure in which the one or more gaps maybe scheduled in any of 100 positions within the frame. The gaps mayoccur at the first position during a first frame, a second positionduring a second frame, and so on. The order of positions at which thesynchronized gap occurs need not be sequential, and may be randomized.The order may be pre-set, or it may be set during operation of the DSAnetwork, such as where a central controller, base station, or othercoordinating device dictates the position of the gap and, therefore, thedetection period, in various frames. Moving the location of one or moregaps within a frame structure changes the detection periods, which mayimprove the likelihood of accurately and quickly detectingnon-cooperative signals. For example, moving the detection periods mayprevent unintentional, and potentially-undetectable, synchronizationwith a non-cooperative frame structure, which may cause the detectionperiod to occur at a time when the non-cooperative system is also nottransmitting. The gap and detection period also may be synchronized tothe synchronicity or frame structure of a known non-cooperative systemor signal, to make sure that the detection period occurs during anexpected transmission time of the non-cooperative system.

Other embodiments may include various changes to the synchronized gaptiming, duration, or other characteristics. For example, the geographicbreadth may be varied to include more or fewer cooperative DSA-enableddevices. The synchronized gap may be implemented on the fly, or it mayoccur at pre-set times or locations within a frame. A synchronized gapmay be used with any DSA-enabled network structure, e.g. infrastructure,ad-hoc, and peer-to-peer type networks.

Since the synchronized gap may be synchronized between all orsubstantially DSA-enabled devices in a region, it also may preventDSA-enabled devices from detecting one another. For example, bydefinition each of the DSA-enabled devices in FIG. 17 is silent duringthe gap period. Therefore, neither DSA-enabled device will detect theother. In principle, the use of a single coordinated detection gap amongall DSA-enabled devices may make it difficult, unlikely, or impossiblefor a DSA-enabled device to join a DSA network, since it will not beable to detect transmissions of DSA-enabled devices in the network and,therefore, will not be able to perform initial communicationcoordination (rendezvous) with the network or receive appropriatecontrol information. An example of a rendezvous process used tocoordinate initialization of communications between a new DSA-enableddevice and an existing DSA network according to embodiments of theinvention is described in further detail below.

To enable DSA-enabled devices in a cooperative network and/or otherDSA-enabled devices with which the detection gap is synchronized todetect one another, a second detection period or periods may be used.FIG. 18 shows an example of a time period in which each of twoDSA-enabled devices uses a second detection period according toembodiments of the present invention. The second detection period may beset by each DSA-enabled device independently, i.e., it may not besynchronized among DSA-enabled devices in the network, and may bereferred to as non-synchronized, asynchronous, randomized, or offset(relative to the synchronized detection period). Randomized timing maybe used since each DSA-enabled device is unaware of specific times atwhich other DSA-enabled devices may be transmitting. Since the detectionperiod is often short compared to the frame length, a random timing mayincrease the chance of detecting other DSA transmissions. As a specificexample, a detection period may be on the order of about 40 μs for aframe length of about 5 to 20 ms. A detection gap may be, for example,400 μs, and the corresponding detection period inside of the detectiongap may be 40 μs. The time before and after the detection period, butinside the gap, may be reserved for frequency changes. Thenon-synchronized detection period may be offset from a detector schedulefor the DSA-enabled device or network as well as being non-synchronizedwith the synchronized detection period shared with other DSA-enableddevices. That is, the detector may not be synchronized with thesynchronized detection period. For example, a detector may detectcontinuously and a signal classifier or other device may be used tofilter out known DSA signals. In general, DSA-enabled devices accordingto embodiments of the invention may use one or more local or separatedetectors, and each detector may or may not be configured to operateduring one or more detection gaps used by a particular DSA-enableddevice or network. In an embodiment, one or more detectors may beoperated continuously, which may require additional processing resourcesthan embodiments in which it is only operated during a detection gap. Inanother embodiment, a DSA-enabled device may include a first detectorthat operates during the synchronized gap period, and a second detectorthat operates during the asynchronous gap period. Other configurationsand combinations of detector operating time periods and detection gapsmay be used.

As shown in FIG. 17, the use of a randomized or offset detection periodby each DSA-enabled device may allow the DSA-enabled device to detectother DSA-enabled devices. For example, at time 710 each DSA-enableddevice 501, 502 may cease transmissions for the coordinated detectiongap. During this time, neither DSA-enabled device 501, 502 will detectthe other (since neither is transmitting), but each may detectnon-cooperative signals. At a second, non-coordinated time 720, thefirst DSA-enabled device 501 may enter a detection mode during which itrefrains from transmitting and detects other signals, including thecooperative signal of the other DSA-enabled device 502. Similarly, atanother time 730 the second DSA-enabled device 502 may be in anon-coordinated detection period, allowing it to detect transmissionsfrom the first DSA-enabled device 501.

In some embodiments, the detection gap and/or non-synchronized detectionperiods may be omitted. Such embodiments may include other techniques toprovide similar features to those typically provided by the detectionperiods. In an embodiment, a physically-separate or stand-alone detectorin communication with the DSA network, such as via a base station, maybe used to detect both cooperative and non-cooperative signals. In anembodiment, a DSA-enabled device may use a much faster detectionsampling rate when sensing communications with a detector than istypically used in embodiments which include detection periods, so as toincrease the odds of detecting a non-cooperative or non-DSA signal thatis not blocked by other DSA transmissions. Such an embodiment may not bepreferred, since the time spent in a detection mode is increased. Insome embodiments in which detection periods are not used, a DSA-enableddevice may spend approximately 10% of each frame detecting and 90% intransmitting or receiving data. In configurations where other DSAsystems use a substantial portion of the channels available to thesystem, detectors may have to sample at a rate up to 2 to 5 timesgreater to detect other signals within an acceptable period of time. Forexample, regulatory, service provider, and/or other requirements mayspecify that a DSA-enabled device stop using a channel within a certaintime after a non-DSA or non-cooperative signal has been detected by theDSA-enabled device, or other channel abandonment requirements. To meetsuch requirements, embodiments that do not use detection periods mayhave to sample at a much higher rate. Since the portion of time theDSA-enabled device spends transmitting data may be decreased, datathroughput for the DSA-enabled device may be substantially decreased.

The use of one or both detection gaps as previously described also mayreduce the “false alarm” rate experienced by a DSA-enabled device withrespect to detecting and identifying non-DSA transmissions. A falsealarm occurs when a DSA-enabled device identifies a detected signal asoriginating from a non-cooperative DSA-enabled device, when the signalactually is from another DSA-enabled device. A false alarm also may becaused due to a false identification of noise as an interfering signal.If there are DSA-enabled devices near each other, the probability offalse alarms for each of the radios may be increased because a detectedDSA signal typically is associated with a relatively low signal-to-noiseratio (SNR), for example 0 to 10 dB. This could cause the DSA-enableddevice to incorrectly identify a DSA signal as noise, or incorrectlyidentify noise as a signal. In some embodiments, these determinationsmay be performed by a signal classifier as described in further detailbelow. A false alarm may adversely impact operation of a DSA-enableddevice or system, by causing the DSA-enabled device to believe that oneor more channels on which the false alarm occurred are being used,causing the DSA-enabled device to abandon the channel. If too many falsealarms occur, the DSA-enabled device may believe that all channels arebeing used, and may stop operating completely. False alarms maypartially or entirely define the amount of spectrum a DSA-enabled devicebelieves is available for use when, much of the time, the spectrum isempty of non-cooperative signals, and the false alarms dominate the DSAdecision process. Since the detection gaps allow DSA-enabled devices tomore accurately identify the presence of cooperative and non-cooperativeDSA-enabled devices as previously described, these gaps also may reducethe corresponding false alarm detection rates.

In another embodiment, one or more signal classifiers may examine datareceived from the detectors to identify detection data containing DSA ornon-cooperative signals Further details regarding the operation ofsignal classifiers according to embodiments of the present invention areprovided in further detail below. If the DSA-enabled device is toconnect to a DSA network at high link distances, and/or operate atrelatively high transmission power levels without causing interferenceto non-cooperative DSA-enabled devices, low detection thresholds may beused. However, a signal classifier may be inaccurate, especially whendealing with low signal-to-noise ratio data or operating at lowthreshold levels. Additionally, in multipath conditions, DSA signals maybe distorted and look similar to non-cooperative signals, such as wherea DSA detector is unable to resolve a multipath signal, causing aDSA-enabled device to unnecessarily abandon a channel that appearsoccupied. An inaccurate signal classifier also may cause more detectiondata to be collected, which may include relatively strongnon-cooperative signals, leading to a higher false alarm rate. As aspecific example, a configuration that does not use the detection gapmay collect about 2 to 5 times more detection samples than a similarsystem that implements a detection gap. The DSA-enabled device mayindicate the presence of about 10 to 100 times more non-cooperativesignals, many of which may represent false alarms.

Different detection gap schemes may be used for radios with differenthardware or operating characteristics. For example, Push-to-Talk (PTT)radios, devices with lower throughput, unsynchronized systems, and/orsystems that cannot perform detection and communicationtransmission/reception concurrently, or that do not have a separatedetector and transceiver at each DSA-enabled device may not be suitablefor use with the detection gap previously described. Embodiments inwhich a synchronized detection gap is not used may allow DSA-enableddevices to communicate at arbitrary times, at the expense of increaseddifficulty in establishing or maintaining communication coordinationamong the DSA-enabled devices, since there may be no reliable way topredict when other DSA-enabled devices in a DSA network will betransmitting and/or detecting.

As a specific example, systems which use a time division duplex (TDD)frame structure may schedule a detection gap based on the TDD framestructure. Most PTT radios do not use a TDD frame structure. However, ithas been found that a DSA network may still use PTT and similar devicesby using periods when the device is not placed into a transmitting modefor detection. Specifically, a PTT radio may perform detection when thetransmit button is not activated by a user.

To minimize the time required for a DSA-enabled device to initially joinan existing DSA network or to establish a new DSA network with one ormore other DSA-enabled devices, a DSA-enabled device may enter a “freewheel mode” in which it continually refrains from transmitting and onlydetects within one or more regions of the spectrum. For example, aDSA-enabled device may increase the amount of detection time bycontinuously calling a detector at different frequencies as it searchesfor a DSA base station or other DSA-enabled device. This may beequivalent to using effectively random detection period timing comparedto frame timings used by any other DSA-enabled devices in the region.

A specific example of a network using detection gaps according toembodiments of the invention is described in further detail in U.S.application Ser. No. 11/582,496, filed Oct. 18, 2006, the disclosure ofwhich is incorporated by reference in its entirety.

Some non-DSA networks use preset channels or a beacon to allowDSA-enabled devices in the networks to communicate. Such techniques maybe unsuitable for DSA networks, especially in conditions in which largespectrum ranges may be available to the network or in which the networkmay be unstable or dynamic due to interference concerns, topologicalconsiderations, and other conditions. Thus, to join DSA-enabled devicesto a particular network, a rendezvous process may be used to coordinatecommunication initiation and maintenance among DSA-enabled devices.

Referring again to FIGS. 1-2, a DSA-enabled device may include acommunication coordinator to perform communication channel selection andcoordinate channel selection and use with other devices in a DSAnetwork. The coordinator may monitor, negotiate, adjust, and maintaincommunication channels among DSA-enabled devices. According toembodiments of the invention, these functions may be performed withoutcausing noticeable interruptions to DSA communications or unacceptableinterference to primary users. The process of initiating and maintainingcommunication among DSA-enabled devices in a DSA network may be referredto as a “rendezvous” or “spectrum state readiness” process.

FIG. 19 shows an example high-level view of a process that includes DSAspectrum sensing, channel selection, communication initialization, andnetwork maintenance according to embodiments of the invention. As shown,the process of selecting and using channels may be a cyclical orcontinuous process. For example, a DSA-enabled device may perform theprocess continually while communicating in a DSA network, with periodsof data transmission and/or reception interspersed with some or all ofthe shown functions. For example, in an embodiment transmission andreception periods may be interspersed with detection and channelchanges. At 3210, the DSA-enabled device may perform spectrum sensing,i.e., detection, in which local spectrum usage is determined. Thisprocess may allow the DSA-enabled device to identify channels or regionsof spectrum that may be available for use by the DSA-enabled device incommunicating with other DSA-enabled devices. At 3220, the DSA-enableddevice may perform channel classification and ranking as describedelsewhere herein. For example, the DSA-enabled device may assign andre-assign channels to channel use tables to indicate whether thechannels are available for use by the DSA-enabled device.

At 3230, the DSA-enabled device may select a channel to use incommunicating with cooperative DSA-enabled devices in the region. TheDSA-enabled device also may select which DSA network to join if itidentifies multiple networks, effectively determining which of thenetworks will be a cooperative network. In some cases, the DSA-enableddevice may be restricted as to which of multiple DSA networks it mayjoin, such as where regulatory requirements or other policyconsiderations specify networks that a DSA-enabled device may or may notjoin. As part of the channel and network selection process, theDSA-enabled device may advertise its presence on one or more channelswhere DSA signals have been detected or that have been identified asempty channels. The DSA-enabled device may then negotiate acommunication channel with other DSA-enabled devices in the DSA network.Quality of service (QoS) constraints also may be applied during thechannel and network selection process at 3230. For example, if a channelwith a high availability is desired, channels where the system hasdetected no noise, a minimal level of noise, or only a low level ofman-made noise may be considered. As another example, a DSA-enableddevice may omit channels at which its antenna performs poorly incomparison to other channels. Further details regarding the process bywhich a DSA-enabled device advertises its presence and joins a DSAnetwork are provided below.

At 3230, the DSA-enabled device may perform network maintenance bymaintaining one or more lists of preferred channels as described herein.If the DSA-enabled device determines that it has become disconnectedfrom the DSA network, i.e., it is no longer receiving expected DSAsignals, it may return to a detection mode 3210 or otherwise restart theprocess shown. At 3250, the DSA-enabled device may re-evaluate thechannel selected at 3240 to verify that it is still an appropriatechannel to use for communicating with cooperative DSA-enabled devices.For example, the DSA-enabled device may examine one or more channelscurrently in use to determine if non-cooperative signals have beendetected.

In some embodiments, the channel selection 3230, network maintenance3240, and re-evaluation 3250 functions may be considered the entirety ofthe rendezvous process. In performing the functions shown in FIG. 19, acommunication coordinator module may interface with other DSA componentssuch as a spectrum manager, a transceiver API, and other components ormodules. For example, the communication coordinator may receive logicalchannel information such as a candidate channel list from a channelmanager, which can be used to negotiate or select a communicationchannel for use by the DSA-enabled device. The coordinator also maymaintain the channel once it is established and manage channel switchingin response to changing interference or network capacity conditionsidentified by a detector and signal classifier.

FIG. 20 shows the structure of an example communication coordinatoraccording to an embodiment of the invention. Arrows in FIG. 20 representdata flows that may occur between modules or other sources. Thecoordinator 124 may include separate modules to perform primaryfunctions of the coordinator. For example, as shown in FIG. 20, thecommunication coordinator may include an initialization/cold startmodule 3325, a channel maintenance module 3335, and a channel switchingmodule 3340. The initialization module 3325 may perform functionsrelated to initial start-up of a DSA-enabled device, or functions that aDSA-enabled device performs when initially seeking to join an existingDSA network. The channel maintenance module 3335 may coordinatecommunication with other DSA-enabled devices on a selected channel. Thechannel switching module 3340 may coordinate movement of the DSA-enableddevice from one channel to another, such as when it is determined thatDSA-enabled devices in a DSA network should cease use of a particularchannel. Each of the initialization, channel maintenance, and channelswitching modes is described in further detail below. In general, thecommunication coordinator 124 will operate in one of these modes at atime. For example, the DSA-enabled device may operate in aninitialization mode when first joining a cooperative network, operate ina channel maintenance mode when communicating with cooperativeDSA-enabled devices in a DSA network, and operate in a channel switchingmode when the DSA-enabled device or network changes communicationchannels. Each of the three corresponding modules may use and applyseparate channel selection criteria so that the DSA-enabled device mayuse different criteria to classify channels when operating in thedifferent modes. For example, in an initialization mode the DSA-enableddevice may search for channels that contain a DSA signal or for emptychannels; in maintenance mode the DSA-enabled device may search forempty channels that could be used if the in-use channel must beabandoned. When decisions regarding communication channels are made,they may be communicated 3365 to a modem, transceiver, detector, orother physical or logical interface 3360 to implement. For example, aradio may be tuned to a new channel as part of a channel switchingprocess.

The coordinator 124 may receive information from various sources, suchas detectors, users, and policymakers via, for example, a spectrummanager. The information may include, for example, channel ranking data,network topology or other radio input, and radio configuration data suchas policy information. This information may be combined withenvironmental information provided by other DSA-enabled devices to makedecisions regarding potential communication channels. For example, thecoordinator may receive channel ranking data that describes theDSA-enabled device's relative preference for certain channels, such asgenerated by a channel manager as described herein. The coordinator alsomay receive network, topology, and radio data 3315 that providesinformation about network conditions. Policy requirements also may bereceived that specify operational constraints for the DSA. Remoterendezvous data, such as information regarding potential channel changesidentified or suggested by cooperative DSA-enabled devices, may beprovided to the channel switching module 3340 for use during channelswitching operations or to initiate a channel move. Data used by thecommunication coordinator may be filtered through a policy module 140 asdescribed with respect to FIGS. 1-2 and be delivered via a configurationinterface 3350. For example, the policy module may identify certainchannels that should not be used, and may accordingly alter the channellist provided to the communication coordinator by the channel manager132. For example, a DSA-enabled device may receive a suggestion of achannel to use for communicating with a remote DSA-enabled device fromthe remote DSA-enabled device. The local policy module 140 may, viaconfiguration interface 3350, indicate that the suggested channel isdisallowed, such as due to historical data indicating non-cooperativeuse of the channel as collected by the local DSA-enabled device. Otherconsiderations may cause the policy module to restrict use of somechannels as described in further detail herein.

The coordinator 124 may store a local decision history 3345 that trackschannel data and channel selections made by the DSA-enabled device forlater use by the coordinator 124. For example, a communication channelmay be selected based on information received from a spectrum manager.Later, it may be determined that the selected channel was undesirable orless than optimal, such as where the spectrum manager did initially nothave data indicating an existing adverse frequency condition in theselected channel. The coordinator may cause the DSA-enabled device tomove to a new channel (i.e., cease use of the initially-selected channeland begin using a different channel), and store the initial decision touse the channel, and the resulting channel change in the local history3345. If the same channel is again indicated as available at a latertime, the coordinator may consult the local history to verify that thechannel is not known to be occupied or otherwise undesirable. Upon doingso, the coordinator may use the previous channel change as evidence thatthe seemingly-available channel is non-optimal and, therefore, mayselect a different channel.

The coordinator also may include a system event watchdog module 3330.The watchdog module may monitor channel data, such as data received andprocessed by the channel maintenance module 3335. Upon detection of anadverse frequency condition, such as detected interference with anon-cooperative device, or detection of a signal indicating the presenceof a non-cooperative device in a chosen channel, the watchdog 3330 mayinitiate a channel change. The watchdog module also may receive messagesindicating a channel change, such as when a signal classifier generatesa channel switch trigger as previously described.

A communication coordinator according to embodiments of the presentinvention may not include each and every module or function described.For example, a local decision history may not be maintained. As anotherexample, a separate or dedicated detector may be omitted, and aDSA-enabled device may instead use a radio for both network detectionand communication with other DSA-enabled devices.

The communication coordinator 124 and each module therein may beimplemented as a general-purpose processor in combination withinstructions stored in a computer-readable storage medium. When theprocessor executes the instructions, it may perform the functions andmethods described. The general-purpose processor also may be transformedinto a special-purpose computing device by implementing theinstructions. The communication coordinator 124 and modules therein alsomay be implemented in a special-purpose processor and/or additionalcircuitry specifically designed to implement the functions and methodsdescribed.

FIGS. 21 and 22 show example process flows for performing DSA discoveryand communication coordination according to embodiments of theinvention. The various steps and functions may be performed by one ormore communication coordinator modules in one or more DSA-enableddevices. FIGS. 21A-C show methods that may be performed by a basestation during communication coordination according to embodiments ofthe invention. FIGS. 21D-F show methods that may be performed by asubscriber unit during communication coordination according toembodiments of the invention. FIG. 22A shows an example of the entirecoordination process for a base station or similar DSA-enabled deviceaccording to an embodiment of the invention. Similarly, FIG. 22B showsan example of the entire coordination process for a subscriber unitaccording to an embodiment of the invention.

FIG. 21A shows an example process for a base station startup modeaccording to an embodiment of the invention. The process may begin, forexample, upon a cold start of the DSA-enabled device. At 3400, theDSA-enabled device may enter a continuous detection, or “free wheel”mode, in which only detection is performed. At 3401, the detectors areprovided with a data link layer frame structure that defines the timingof detections to be performed by the detectors. At 3402, a list ofdisallowed channels may be received from a policy manager or othersource of policy information, which indicates channels or spectrumregions that the DSA-enabled device is not allowed to use for DSAcommunications, such as for regulatory, geographic, or other reasons asdescribed herein. The detectors may be tuned to the appropriate channelsas specified in the frame structure at 3403. At 3404 the detectors mayscan the spectrum ranges associated with the channels one or more times.As described in further detail below, at 3404 potential signals detectedby the detectors may be filtered through a signal classifier, such as byusing one or more signal masks, to identify specific signals or types ofsignals. Where a channel is scanned multiple times, a signal maskcomparison may be applied for each scan. Based on data received from thedetectors, classification information and decisions, and policyrequirements, a list of potential channels to be used for DSAcommunications may be generated and ranked at 3405. Examples of criteriaapplied to rank channels include threshold requirements that mayindicate whether detected energy represents noise or a signal, detectorthreshold (the amount of energy required for a detector to indicate thepresence of a signal), user preferences, preferences set by a regulatoryagency, network coverage, and propagation characteristics of certainspectral regions. As a specific example, a channel may be required tohave energy measurements below a certain level for a specified number ofconsecutive measurements before the channel is considered to beavailable for use by the DSA system. Other criteria may be applied.Further details regarding the process of ranking channels is describedin further detail below.

At 3406, a preferred channel may be selected. The preferred channel isthe channel the DSA-enabled device has identified as being the preferredmatch to the ranking criteria and policy requirements. Differentselection modes may be used. That is, the communication coordinator mayuse different methods to select a preferred channel from multiplechannels that meet the selection criteria and policy requirements.Examples of different selection modes include selecting a random,non-occupied channel, selecting the lowest-frequency non-occupiedchannel, selecting a channel in which the least total energy wasdetected, and selecting a channel that is least-occupied over a giventime period. Other selection modes may be used. At 3407, the DSA-enableddevice may verify that the preferred channel is not “blocked” from beingused. For example, historical channel data may be consulted to verifythat the selected preferred channel is not actually available orotherwise is a poor choice for use by the DSA-enabled device. The use ofhistorical channel data is described in further detail herein.

At 3408, the DSA-enabled device's radio may be set to operate on theselected channel, i.e., to send and receive DSA communications on thatchannel. The DSA-enabled device may then send an initial packet at 3409.In some embodiments, the initial packet sent by a base station mayinclude an ID of the base station, the preferred channel, the number ofDSA-enabled devices operating on the channel of which the base stationis aware, the number of candidate channels identified at 3405, the listof candidate channels identified at 3405, the rankings of channelsgenerated at 3405, information about the DSA-enabled device'sgeographical location (e.g., latitude and longitude of the DSA-enableddevice), and combinations thereof. Other data may be included. Aftertransmitting the initial packet at 3409, the DSA-enabled device mayenter a channel maintenance mode.

FIG. 21B shows an example process for a base station operating in achannel maintenance mode according to an embodiment of the invention. At3410, the DSA-enabled device may periodically send Keep Alive and/orAdvertise Request packets. In general, these packets may be sent to allDSA-enabled devices in a network or in a geographic region, or may bebroadcast generally for reception by any DSA-enabled device capable ofreceiving them. Such packets may be used, for example, to keepsubscriber units informed about the channel environment (such aspreferred channel, known DSA channels, channel list, etc.) as detectedby the base station. For example, a Keep Alive packet typically providesnetwork information from the sending DSA-enabled device's perspective toother DSA-enabled devices in the network, such as when a base stationprovides network information to subscriber DSA-enabled devices.Advertise requests typically may request data from other DSA-enableddevices, such as when a base station requests subscriber DSA-enableddevices to provide network or other data to the base station. ADSA-enabled device that is attempting to connect to a base station mayattempt to decode received packets to determine if they have been sentby a base station and, if the DSA-enabled device is able to decode thepacket, may then analyze it to determine whether the address of thesending base station matches a desired address. For example, a signalclassifier in the DSA-enabled device attempting to join a DSA networkmay identify an Advertise Request packet as having been sent by aDSA-enabled device.

As described in further detail elsewhere herein, the informationprovided in the packets sent by the base station may be stored in aneighborhood data structure maintained by other DSA-enabled devices inthe DSA network. In some embodiments, control packets (including KeepAlive, Advertise Request, and other control packets) may be sent on thesame channel or channels as data packets. In other embodiments, separatecontrol channels may be used. At 3411, when the DSA-enabled devicereceives a response to an Advertise Request, it may update storedinformation regarding DSA-enabled devices in the network at 3412 andcontinue periodically transmitting Keep Alive and Advertise Requestpackets. For example, the response may indicate that a new DSA-enableddevice has joined the network, and the base station may update the listof DSA-enabled devices in the network. If a non-cooperative radio isdetected at 3413 or if a reset packet is received from a DSA-enableddevice in the network at 3420, the base station may enter achannel-switching mode 3414. A reset packet may be sent by a DSA-enableddevice in the network, for example, if the DSA-enabled device detects anon-cooperative DSA-enabled device using the preferred channel. It willbe understood that the reception of an Advertise Request response,detection of a non-cooperative device and/or reception of a reset packetmay not occur, may not occur at any particular time, and may not occurin any particular order. Thus, the specific flow shown in FIG. 21B isintended only as an example.

During a channel maintenance mode, a DSA-enabled device may detect aproblem with the current operating channel. Examples of problems thatmay occur with a channel include conditions such as lost neighbors(DSA-enabled devices previously in the network that leave unexpectedly),an empty channel, detection of a non-cooperative signal on a channelbeing used by the DSA-enabled device, or a channel for which the DSAcommunications may be expected to cause interference, and other adverseconditions. Detecting a non-cooperative radio may cause the base stationto designate the current operating channel as in use by a non-DSAsystem. In the case of a lost neighbor, the base station mayperiodically cycle through clear channels and transmit Keep Alivepackets to attempt to relocate the missing DSA-enabled device. In anembodiment, detecting a non-cooperative device, identifying a potentialfor interference on a current channel, or otherwise detecting an adversecondition may cause the base station to enter a channel switching mode.

FIG. 21C shows an example process for a base station operating in achannel switching mode according to an embodiment of the invention. At3430, the base station may transmit an Advertise Request upon detectingan adverse condition such as a non-cooperative signal. At 3431 the basestation may then wait a period of time to receive one or more AdvertiseReplies from other DSA-enabled devices in the network at 3432. In anembodiment, the base station may wait a set period of time to receivereplies. Advertise Replies may include available channel informationbased on spectrum detections performed by other DSA-enabled devices inthe network and, therefore, may provide the base station the latest viewof available channels as detected by the subscriber units. For example,Advertise Request responses may include channel preferences or rankedchannel information from the responding DSA-enabled devices. At 3433,the base station may identify a new preferred channel and determinewhether the new preferred channel is the same as a currently-usedchannel. For example, the base station may select an available channelthat is most common to or preferred by a majority of or all otherDSA-enabled devices that respond to the Advertise Request. The currentchannel may not be identified as the preferred channel, for example,when one or more DSA-enabled devices has sent a reset signal, or where anon-cooperative signal has been detected on a channel being used by thenetwork. The current channel may be identified as the preferred channel,for example, when detected non-cooperative interference is limited to arelatively small number of DSA-enabled devices in the DSA network, inwhich case such DSA-enabled devices may disconnect from the network. Inan embodiment, the base station also may select a channel that isunavailable to one or more DSA-enabled devices but is preferred forother DSA-enabled devices in the network, which may cause thoseDSA-enabled devices for which the selected channel is unavailable todisconnect from the network.

In an embodiment, a channel comparison algorithm may be used to find ahighest statistically-scored channel among the currently-active orresponding DSA-enabled devices. For example, each DSA-enabled device ina DSA network may maintain a ranked list of locally-preferred channels.When a channel change is indicated, the base station may request theseranked lists from the other DSA-enabled devices in the network, comparethe ranked lists to each other and to the base station's ranked list,and select a common preferred channel using a statistical algorithm. Asa specific example, in some embodiments, the following general algorithmmay be used:

1, For each region of spectrum or set of channels, at each channelwithin the region not being used by the DSA-enabled network, the qualityof the channel is recorded and the number of cooperative devices thatcan use the channel is counted.2. If more devices can use this channel than the previously-selectedchannel, or the channel is wider and can be used by at least as manydevices as the previously-selected channel, or the channel is ahigher-quality channel than the previously-selected channel, then selectthis channel.3. Otherwise, continue using the present channel and repeat 1-2 for thenext channel or region of spectrum.

If the current channel is identified as the new preferred channel, andthe base station did not initiate the channel switching procedurebecause it detected a non-cooperative signal, communication may bemaintained on the same channel and the base station may send a channelswitch request at 3434. If unable to change to the new channel, one ormore devices in the network may leave the network to avoid interferencewith non-cooperative signals as previously described. If the channelchange results from an adverse condition detected by or caused by thebase station, the base station may select the next preferred channel at3435 and base station may transmit a Channel Switch Request packet toDSA-enabled devices in the network at 3434 to notify them of the newoperating channel. The current channel may be used to send informationabout the newly-selected channel. After sending a channel switchrequest, the base station may wait a finite amount of time at 3436before re-tuning its own radio to the new operating channel to transmitand receive data, and then enter a channel maintenance mode at 3437. ADSA-enabled device that receives the channel switch request may changeits operating channel accordingly and may also enter a channelmaintenance mode.

FIG. 21D shows an example process performed by a subscriber DSA-enableddevice operating in a start-up mode according to an embodiment of theinvention. The DSA-enabled device may start at 3441 with one or moredetectors in a “free-wheel,” or continuous detection, mode. Thedetectors may detect energy in one or more channels. A DSA signal maskmay be applied to the detected energy at 3442 to identify detected DSAsignals. At 3443, the DSA-enabled device may select a channel thatappears to have DSA or cooperative transmissions, and tune its own radioto the channel at 3444. A network identifier may be obtained from apacket received on the selected channel at 3440. The identifier mayindicate, for example, the identity of a base station or othercooperative DSA-enabled device in the network. The subscriberDSA-enabled device may retrieve a desired base station identifier and/ora preferred operating frequency or channel from a file, or it may obtainor calculate this information based on observed or received signals. Ifthe identifier in a received packet matches a desired or allowednetwork, the DSA-enabled device may then join the network. In anembodiment, the DSA-enabled device may be configured to use one or morepre-defined networks, each of which may have a unique networkidentifier. Control information, such as included in a Keep Alivepacket, may be transmitted according to a known modulation and data rateformat to allow DSA-enabled devices to retrieve the identifier. Forexample, a modulation scheme may be defined for DSA packet headers, andduring operation a packet header may contain a description of themodulation used for the remainder of the packet. A DSA-enabled devicealso may use an analysis scheme, such as constellation analysis, todetermine the modulation scheme used for a received packet, and operateon that scheme while processing the packet. A DSA-enabled device alsomay operate using its own modulation scheme in response to receiving apacket from another DSA-enabled device, thus placing the burden on theother DSA-enabled device to change modulation schemes to match.DSA-enabled devices also may be able to operate in multipleconfigurations, one of which is selected by the base station. To join anetwork, the DSA-enabled devices may try each of the pre-determinedconfigurations until they are able to successfully retrieve the networkidentifier from a received packet. Pre-defined modulation schemes alsomay be used for beacon signals. When a DSA-enabled device locates such asignal, the presence of the beacon signal and corresponding modulationscheme would strongly indicate the presence of another DSA-enableddevice. Similarly, a DSA-enabled device may be configured to search forcooperative devices on one or more pre-defined channels or regions ofspectrum, for example to enable a DSA-enabled device to rapidly locate acooperative base station when initializing from a cold start.

Still referring to FIG. 21D, after finding and identifying a basestation based on identification of a cooperative signal, the subscribermay send a synchronize packet (SYN) to the base station at 3445. TheSynchronize packet may contain the same or similar channel informationas contained in a Keep Alive packet, such as channel usage data observedor measured by the subscriber DSA-enabled device. For example, it maycontain the DSA-enabled device's preferred channel, known cooperativechannels that have been detected by the DSA-enabled device, knowncooperative channels that have been cleared by a policy module fortransmission or cleared for transmission at certain power levels, a listof known channels, or combinations thereof. The channels may be rankedby preference, and more than one channel may be listed. After sendingthe SYN packet at 3445, a subscriber DSA-enabled device may wait toreceive an Acknowledgement (ACK) packet from the base station. The ACKmay contain a preferred channel on which the subscriber DSA-enableddevice should operate. It may also contain other channel information. Ifthe subscriber device receives an acknowledgement from a cooperativebase station at 3446 (i.e., a base station with which the subscriberdevice is allowed or configured to form a cooperative network), thesubscriber DSA-enabled device may enter a channel maintenance mode at3450. If no ACK packet is received after a certain time, the DSA-enableddevice may conclude that there is not a cooperative base station on theselected channel, and/or that the packet received at 3440 is not from anetwork the DSA-enabled device can join. The DSA-enabled device then maylook for another DSA packet, such as a packet having a different networkor base station ID at 3440, and/or the DSA-enabled device may selectanother channel 3443 on which it previously identified a cooperative orpotentially-cooperative transmission. For example, if the DSA-enableddevice has detected another potential DSA-enabled network on the samechannel or channels at 3447, it may return to 3440 to obtain a newnetwork ID. Otherwise, it may return to 3443 to identify a new channelthat has a potential cooperative signal.

FIG. 21E shows an example process performed by a subscriber DSA-enableddevice operating in a channel maintenance mode according to anembodiment of the invention. After tuning its radio to operate at apreferred channel at 3450 selected by a base station as previouslydescribed, the DSA-enabled device may send data packets to theassociated base station, and may periodically send a Keep Alive packetto the associated base station at 3451. The subscriber DSA-enableddevice also may respond to an Advertise Request received from the basestation at 3452 by sending an Advertise Reply packet at 3453 aspreviously described. Advertise Reply packets may provide channelinformation obtained by the subscriber DSA-enabled device, so as toinform the base station of the channel environment as detected by thesubscriber unit. The channel information may include, for example, alist of channels locally preferred by the DSA-enabled device, known DSAchannels, a candidate channel list, and other data. This information maybe stored in a neighborhood data structure at the subscriber unit and/orat the base station, and may be used during channel switching operationsas previously described. It will be understood that the reception of anAdvertise Request response, detection of a non-cooperative device and/ordetection of a lost neighbor or empty channel may not occur, may notoccur at any particular time, and may not occur in any particular order.Thus, the specific flow shown in FIG. 21E is intended only as anexample.

During the channel maintenance mode, the subscriber DSA-enabled devicemay detect a problem with the current operating channel at 3454 and3456. Examples of problems that may occur with a channel includeconditions such as lost neighbors (i.e., unexpected absence of aDSA-enabled device previously in the network), an empty channel,detection of a non-cooperative radio signal, and other adverseconditions. Upon detecting an adverse condition at 3454, the DSA-enableddevice may send a reset packet at 3455.

Different adverse conditions may cause the DSA-enabled device to takevarious actions or enter other modes. For example, if the DSA-enableddevice detects a lost neighbors or an empty channel, the DSA-enableddevice may enter a startup mode, such as the mode described with respectto FIG. 21D. If the DSA-enabled device detects a non-cooperative radioor signal, it may enter a channel switching mode.

FIG. 21F shows an example process for a subscriber DSA-enabled device ina channel switching mode according to an embodiment of the invention.The subscriber DSA-enabled device may send a Reset packet at to the basestation at 3460 upon detecting a non-cooperative signal or other adversecondition as previously described. The Reset packet may include spectrumusage information, information about the subscriber DSA-enabled device'schannel preferences, or other data. The base station may send anAdvertise Request that is received by the DSA-enabled device at 3470. Aspreviously described, the DSA-enabled device may send an Advertise Replyat 3462 that is received by the base station and used to determine acommon channel among the subscriber unit channel lists. After selectinga channel, the base station may send a Channel Switch Request, changethe current communication channel, and transition back to a channelmaintenance mode as previously described. A subscriber DSA-enableddevice may receive the Channel Switch Request at 3480 and tune its radioto the new communication channel accordingly at 3464. The subscriberDSA-enabled device may then return to a Channel Maintenance mode.

It will be noted that although various packets used during thecommunication coordination processes are referred to herein usingspecific names, these names may not describe any specific function orcontent of the various packets. For example, a keep-alive packet or asynchronize packet may contain additional information, such as channelor frequency information, DSA-enabled device channel preferenceinformation, detected environmental conditions, or other data.

FIGS. 23A-D show example message flows for communication coordinationaccording to embodiments of the invention. FIG. 23A shows an examplecommunication flow between a base station and a subscriber DSA-enableddevice during a startup sequence. In a base station startup sequence3500, a base station 3501 may select an initial channel on which toconduct DSA communication at 3503 and begin sending Keep Alive or beaconpackets 3504, as previously described. A subscriber DSA-enabled device3502 may begin by performing spectrum detection (scanning) a geographicand/or spectral region for energy. The subscriber DSA-enabled device maydetect and decode a packet sent by the base station at 3504 and identifythe base station or DSA network based on information in the packet at3508. The subscriber DSA-enabled device may then tune its radio to achannel specified in the packet 3504 and join the DSA network at 3510.In a subscriber DSA-enabled device startup sequence 3520, the subscriberDSA-enabled device may obtain a network identifier from a Keep Alive orbeacon signal at 3522, and send a Synchronize (SYN) packet to the basestation at 3524. The base station may reply with an Acknowledgement(ACK) at 3526, at which point the subscriber DSA-enabled device enters asteady state mode at 3528 in which it can send and receive data withinthe DSA network.

FIG. 23B shows an example communication flow between a base station anda subscriber DSA-enabled device during channel maintenance. Aspreviously described, the base station 3501 may periodically send KeepAlive packets 3532, 3536 and Advertise Request packets 3534, 3538 to thesubscriber DSA-enabled device 3502, and the subscriber DSA-enableddevice may periodically send Keep Alive packets 3531, 3537, and/or 3543,and Advertise Reply packets 3535, 3539 to the base station, with theAdvertise Reply packets being sent in response to Advertise Requestpackets. The Advertise Request packets may provide the BS with channelenvironment information, such as one or more locally-preferred receivefrequencies, known DSA channels, a candidate channel list and othernetwork information as seen by the subscriber DSA-enabled device. EachDSA-enabled device may measure one or more time periods 3541, 3542,which may be used to determine whether a DSA-enabled device has becomedisconnected from the network. For example, the base station 3501 maymeasure the time period between sending a Keep Alive packet 3532 andreceiving a Keep Alive packet 3537 from the subscriber DSA-enableddevice 3502. If the period 3541 exceeds a certain time limit, the basestation may determine that the subscriber DSA-enabled device 3502 is nolonger available, may cease communicating with the subscriberDSA-enabled device (such as to avoid engaging in unacceptably-delayedcommunications), or may take other action with respect to theDSA-enabled device. As another example, a time period 3542 may indicatehow often a DSA-enabled device sends a Keep Alive packet even in theabsence of a request from the base station. Similarly, a time period3544 may indicate how often the base station sends a Keep Alive packetto the subscriber DSA-enabled device. Other combinations of Keep Alivepackets, Advertise Request/Reply packets, and associated time periodsmay be used.

FIG. 23C shows an example communication flow between a base station anda subscriber DSA-enabled device during channel switching initiated by asubscriber DSA-enabled device. As previously described, a subscriberDSA-enabled device may detect a non-cooperative signal or other adversecondition at 3552, and send a reset packet 3554 so indicating to thebase station. In response, the base station may send Advertise Requestpackets 3556 to DSA-enabled devices in the cooperative network. During aperiod of time 3557, the base station may receive Advertise Replypackets 3558 from some or all of the DSA-enabled devices in the network.Replies received after the wait period 3557 ends may be discarded orignored, or otherwise given less consideration by the base station.Based on channel preference data in the received Advertise Replypackets, the base station may determine whether the channel on which thenetwork is communicating should be changed at 3559. A channel switchrequest 3560 may then be used to notify subscriber DSA-enabled devicesof a change to the operating channel. The base station may wait on theprior channel for a relatively short period of time 3561 after sending acommand to switch channels, after which the radio will be ready toperform the next operation.

FIG. 23D shows an example communication flow between a base station anda subscriber DSA-enabled device during channel switching initiated by abase station. As previously described, and similar to the processdescribed with respect to FIG. 23C, a channel switch may be performeddue to a non-cooperative signal or other adverse condition detected at3570 by the base station. The base station may send Advertise Requestpackets 3572 to DSA-enabled devices in the cooperative network andreceive Advertise Reply packets 3574 from some or all of the DSA-enableddevices in the network during a response wait period 3573. Repliesreceived after the wait period 3573 ends may be discarded or ignored, orotherwise given less consideration by the base station. Based on channelpreference data in the received Advertise Reply packets, the basestation may determine whether the channel on which the network iscommunicating should be changed at 3575. A channel switch request 3576may then be used to notify subscriber DSA-enabled devices of a change tothe operating channel. Subsequently, the base station may perform aflush of RF data at 3577.

Although not shown, it will be understood that DSA-enabled devices inthe DSA network may operate to transmit and receive data during theprocesses shown in FIGS. 23B-D. In some embodiments, the same channelsmay be used for control packets (Keep Alive, Advertise Request, etc.)and data packets. In other embodiments, dedicated control channels maybe designated and separate channels may be used for data transmissions.

In an embodiment, a DSA-enabled device may perform spectrum sensing andonly subsequently tune to, and decode transmissions received on channelswhere signals are detected. For example, referring to FIG. 21D, aDSA-enabled device may detect and identify signals at 3441-3443 prior totuning to a particular channel. That is, the DSA-enabled device mayfirst look for energy, and then only attempt to send or receive packetswhere energy has been detected. Such an embodiment may be particularlysuited to environments in which regions of the local spectrum are mostlyempty, since it has been found that approaches which assume amostly-used spectrum may generate an unacceptable rate of false alarms.Such embodiments also may be particularly suited to DSA-enabled devicesthat incorporate detectors in lieu of modems since the detector maysimply look for energy without attempting to demodulate every potentialsignal.

In general, the spectrum and channel data exchanged among DSA-enableddevices, such as via Advertise Request/Reply and Keep Alive packets, mayinclude any relevant spectrum usage data. For example, a DSA-enableddevice may provide data regarding specific measurements made by theDSA-enabled device's detectors (e.g., −92 dBm measured at a particularfrequency or channel); derived information regarding spectrum usage(e.g., channels 1-4 are in use by a TV transmitter); policy, regulatory,or other restrictive information (e.g., channels 5-8 are prohibited inthe DSA-enabled device's region); local equipment information (e.g., alocal detector RF filter is malfunctioning or the DSA-enabled device isunable to detect in a certain spectral region); logical channel data(e.g., logical channel 7 is 35-to-37 MHz) or any other spectrum dataavailable to the DSA-enabled device.

Different protocols may be used to select a preferred channel, such asduring a channel-switching process. In an embodiment of the presentinvention, a hand-shaking approach may be used in which cooperativeDSA-enabled devices collectively select a preferred channel before theDSA-enabled devices switch to the new channel. Such an approach may bepreferred when a relatively small percentage of the potential spectrumis available for use by the DSA network, so that a suitable channel ischosen efficiently. In another embodiment, each DSA-enabled device maydecide to switch to a new channel that is selected only by thatDSA-enabled device. This approach may be preferred where a relativelylarge amount of spectrum, such as 90% of potential spectrum, isavailable for use by the DSA network, since channel switches are notvery likely to cause interference with non-cooperative signals.

Although described above with respect to a base station and subscriberDSA-enabled devices, in some embodiments the rendezvous processesdescribed also may be used to form an ad-hoc network, i.e., one withouta pre-determined or fixed base station. For example, if a DSA-enableddevice does not detect any DSA signals in a region, or does not detectan appropriate DSA signal, it may begin operating using the methodsdescribed for a base station. Subsequent DSA-enabled devices in theregion may then detect and identify signals from the first DSA-enableddevice as being from a base station, and operate using the methodsdescribed for a subscriber DSA-enabled device. Multiple DSA-enableddevices in a region may operate as base stations, which may be in thesame or different cooperative networks. In some embodiments, aDSA-enabled device may include hardware, computer-readable instructions,or both to enable the DSA-enabled device to operate as described forboth a base station and a subscriber DSA-enabled device. As anotherexample, in a non-base station configuration, a DSA-enabled device mayrandomly select between operating as a base station or as a subscriberDSA-enabled device. If a base station mode is selected, the DSA-enableddevice may advertise itself and wait for subscriber DSA-enabled devicesto join its network. If a subscriber operating mode is selected, theDSA-enabled device may search for a base station DSA-enabled device andjoin a network established by the base station as previously described.

In an embodiment, a DSA-enabled device may maintain a “channel typephonebook” that matches potential networks or networks observed in aparticular region to channels on which the networks operate. Forexample, different networks may be used by different civic services(fire, police, emergency, etc.) in a region. A DSA-enabled device maymaintain a list of network identifiers associated with each service.During operation, the DSA-enabled device may track the networkidentifiers observed in the area and maintain a list of DSA and/ornon-DSA channels used by each network/service. A user of the DSA-enableddevice then may set the radio to operate with a particular service,without being required to know or identify which channels are used bythe desired service. This also may allow the channels used by eachservice to change dynamically to address immediate needs of eachservice.

The preceding description of communication coordination referred to asingle base station and a number of subscriber DSA-enabled devices. Asmore DSA-enabled devices are added to a DSA-enabled network, multiplebase stations may be used to coordinate communication among theDSA-enabled devices. A DSA cluster may be defined as a local grouping ofDSA-enabled devices that perform coordinated sensing and channelplanning to maintain connectivity with other members of the group. ADSA-enabled network may include multiple clusters. Once established, aDSA-enabled network may support or implement other types ofcommunication between DSA-enabled devices as may be used in othernetworks, such as multicast messages, broadcast messages, and othertechniques.

FIGS. 24A and B show schematic illustrations of multi-cluster networksaccording to embodiments of the invention. DSA-enabled devices in thenetwork may be defined as unattached (filled square), single-cluster(open circle), multi-cluster (filled triangle), cluster leader (filledcircle), and cluster leader/multi-cluster member or “dual-state” (filleddiamond). A multi-cluster member may be referred to as a bridgeDSA-enabled device or as being in a bridge state. A bridge DSA-enableddevice may observe the detection gap for each DSA cluster to which itbelongs, and synchronize the detection gap with one or more clusters. Anetwork may include multiple bridge DSA-enabled devices, and eachcluster may include multiple bridge DSA-enabled devices that connect thecluster to multiple other clusters. A dual-state DSA-enabled device mayremain dual-state temporarily when leaders (typically base stations)come within connectivity range of each other and establish a connection.A dual-state DSA-enabled device may attempt to change its status fromdual-state to reduce the processing workload on the DSA-enabled device.

A DSA-enabled device may change its definition in response to changes inits local environment. An unattached DSA-enabled device may perform asubscriber DSA-enabled device communication coordination process aspreviously described to join one or more DSA-enabled networks. Anunattached DSA-enabled device also may perform a base stationcommunication coordination process as previously described, such as tostart a new DSA-enabled network. The new DSA-enabled network then mayconnect to existing DSA-enabled networks via one or more bridgeDSA-enabled devices, or may remain a separate network.

As previously described, multiple DSA-enabled networks may operatewithin the same geographic region, and may be cooperative ornon-cooperative with the other DSA-enabled networks in the region.Multiple DSA-enabled networks in a region may interfere with eachother's attempts to perform detections. In some embodiments of theinvention, DSA-enabled networks may perform a process called “gapsynchronization.” Gap synchronization may permit multiple DSA-enablednetworks to observe the DSA signals of other DSA-enabled networks in aregion, and mutually adjust the timing of their detection gaps tocoincide. Synchronization of detection gaps may allow a larger number ofDSA-enabled networks to operate in a region while maintaining sufficientdetection sensitivity to satisfy policy requirements.

In an embodiment, each DSA-enabled network may divide its frame into anumber of slices, for example as defined by a parameter n_slice. EachDSA-enabled network may schedule its gap within each frame using arandomly-seeded, pseudo-random sequence (prs) of length n_prs, which isused to determine the location of the gap within the frame, for examplein the range of 1 to n_slice or 0 to n_slice-1 for O-based locations. Inan embodiment, each DSA-enabled network stores a parameter g_oft whichdescribes the current position of the network's gap within thepseudo-random sequence. Each network may start with a randomized valueof g_oft. This may result in gaps that are not initially synchronizedbetween DSA-enabled networks. Alternative gap scheduling techniques maybe used, including schemes that provide a set of known values, includingone or more predefined values for the random seed, pseudo-randomsequence, or starting gap position (g_oft). Alternatively, apseudo-random sequence generator, random number generator, or othertechnique for producing sequences of random values may be used. Anexample 0-based pseudo-random gap schedule of length (n_prs=20) for aframe divided as given by (n_slice=20) is:

[11, 16, 3, 17, 19, 15, 9, 12, 5, 10, 7, 8, 13, 0, 18, 6, 1, 2, 4, 14]

In an embodiment, each DSA-enabled network may independently scheduleits gap on a frame by frame basis, on a slice identified by a locallydefined g_oft'th entry of the pseudo-random gap schedule sequence, thenincrements of (g_oft modulo n_prs). The length of the pseudo-random gapschedule may not affect the speed of convergence for the networks, i.e.,the rate at which the networks achieve a synchronized gap when startingfrom an unsynchronized condition.

In an embodiment, each DSA-enabled device that is part of a DSA-enablednetwork may calculate a transmission schedule for frames for thenetwork. The device also may schedule the network's gap within thatframe according to the current value in the pseudo random sequence (prs[g_oft]). From the transmission schedule, the DSA-enabled device maydetermine when the device should refrain from transmitting, performenvironmental sensing (i.e., within a gap), and/or transmit. If aDSA-enabled device detects another DSA-enabled network's transmissionduring the gap, it considers the detection a failure and records thatresult. The device may also notify other devices in the DSA-enablednetwork of a detection failure in accordance with processes describedelsewhere.

In an embodiment, each DSA-enabled network may maintain a history windowof length n_fail_hist, in which the network or one or more devices inthe network stores an indication of the success or failure of its mostrecent detection attempts. This history may be used by the DSA-enablednetwork to make decisions about when to attempt to adapt its gapschedule to those of neighboring DSA-enabled networks. The history mayalso be used to infer the gap schedules in use by neighboringDSA-enabled networks.

In an embodiment, when the failure ratio within the history window risesabove a certain level, the network may invoke a predictor to calculate anew gap schedule. In an embodiment this may involve computing a newvalue of g_oft. The predictor may analyze the collected history data toestimate a new gap schedule that coincides with those of neighboringDSA-enabled networks. The predictor may use one of several techniques toencourage convergence to a common gap schedule. For example, it may usethe modal gap schedule of the network's neighbors if one exists orotherwise the gap schedule of the network's nearest neighbor. Thepredictor may be imperfect and may be modeled as having an accuracygiven by p_pred.

In an embodiment, each DSA-enabled network may decide whether toreadjust its gap schedule every n_adapt_period frames. Gap schedules mayconverge more rapidly if networks begin counting this period at arandomized offset relative to each other, because two adjacent networksattempting to adapt their gap schedules at the same time may reduce therate of convergence. Experimental results indicate that the size ofn_adapt_period is, in part, responsible for the speed at which thenetwork converges upon a common gap. Using a longer period makes thealgorithm converge more slowly. Using a shorter period makes thealgorithm fail to converge. As a specific example, an adaptation periodof 100 detections may cause the gap to converge relatively slowly.

In some embodiments, the process of gap synchronization among multipleDSA-enabled networks as described here also may permit DSA-enableddevices to automatically synchronize their gap when combining as part ofan ad-hoc network.

A system of DSA-enabled networks in a region may be modeled in terms ofan undirected graph with each node in the graph representing a networkin the system, in which an edge exists between nodes if the two networkslie within a detection interference radius such that one network cannotsuccessfully detect while the other is transmitting. Using this graphmodel, groups of adjacent DSA-enabled networks may be described in termsof clusters of nodes and the neighbors of each node. Furthermore, theconvergence of networks onto the same gap schedule can be modeled as thepropagation of an abstract value (representing a particular gapschedule) through the graph. The parameter g_oft is one possiblemanifestation of this abstract value.

Experimentally, a set of 10 DSA-enabled networks were simulated asrandomly placed in an area of 100×100 arbitrary units (a.u.), with adetection interference radius of 25 a.u. Each node was presumed to havea duty cycle of 30%. The frame was split into 20 slices, and thepseudo-random gap schedule set at a length of 20 a.u. The parametern_adapt_period was set to 10, indicating that each network reevaluatedits gap schedule every 10 detections. The failure threshold at which thenetwork invoked the predictor was 30%. The results of the simulationover 500 frames with no synchronization are shown in the table below:

Failure Net # X Pos Y Pos Gap Offset Ratio (overall) Neighbors 0 32.8192.69 0 0.32 9 1 10.20 58.43 16 0.70 3, 4, 5 2 84.99 2.42 1 0.70 6, 7, 83 10.87 65.98 11 0.52 1, 5 4 21.28 39.92 3 0.28 1 5 15.06 73.19 14 0.481, 3 6 67.76 2.58 5 0.69 2, 7, 8 7 81.45 2.41 17 0.68 2, 6, 8 8 74.2513.86 16 0.71 2, 6, 7 9 34.16 97.95 16 0.33 0

As shown, the networks were found to make no attempts to synchronizetheir gaps. It was found that the failure ratio rises rapidly with thenumber of neighbors in each cluster of networks. For a network in agiven cluster, the failure ratio is roughly equal to 1-(1-d_net)̂n, wheren is the number of neighbors that network has in the cluster and d_netis the duty cycle of the network. In a cluster where one network hasthree other neighbors, the failure ratio was found to be 0.68-0.71.

In another experiment, a simulation was run using the same networktopology and the gap synchronization technique as previously described.As shown in the table below, it was found that the networks synchronizedtheir gaps rapidly even when an inaccurate predictor was used. It wasfound that nearly perfect synchronization may be achieved within about250-500 frames, and that the ratio of failed detections is drasticallyreduced once the system converges, falling to 0.00-0.10 within thebiggest cluster. The table below shows the results for an experiment runover 500 frames with the synchronized gap technique previouslydescribed:

Failure Net # X Pos Y Pos Gap Offset Ratio (recent) Neighbors 0 32.8192.69 4 0.00 9 1 10.20 58.43 16 0.10 3, 4, 5 2 84.99 2.42 1 0.00 6, 7, 83 10.87 65.98 16 0.00 1, 5 4 21.28 39.92 17 0.20 1 5 15.06 73.19 16 0.001, 3 6 67.76 2.58 1 0.00 2, 7, 8 7 81.45 2.41 1 0.00 2, 6, 8 8 74.2513.86 1 0.00 2, 6, 7 9 34.16 97.95 4 0.00 0

FIGS. 24C and 24D illustrate example network diagrams of theunsynchronized case and the synchronized case, respectively, and theconvergence behavior of the networks when a gap synchronizationtechnique according to embodiments of the invention is used. In thesefigures, the number in parentheses after the network name is theinstantaneous value of g_oft after 500 frames. Each different value ofg_oft represents a different gap synchronization domain. FIG. 24C showsthat when there is no synchronization, adjacent networks may havedifferent values of g_oft and thus unsynchronized gap schedules. Thislack of synchronization may result in a high rate of failed detectionsas shown above. In FIG. 24D, nearly all the adjacent nodes have the samevalue of g_oft, and are thus operating with synchronized gap intervals.

In general, if two clusters in a DSA-enabled network operate ondifferent channels, the devices in each cluster will not exchange datawith devices in the other clusters. To assess operation of DSA nodes inthis situation, a simulation was performed in which nodes dynamicallydiscovered available networks, and then decided whether to merge theseparate clusters (i.e., one or both clusters would switch so both usedthe same channel), or to create dynamic gateway “bridge” devices toconnect the clusters operating on different frequencies. This type ofbridging may be performed as a non-network layer function abstractedfrom other network protocols, or it may be integrated with existingnetwork discovery/routing protocols such as an optimized link-staterouting (OLSR) protocol.

FIG. 24E shows the network topology used in the simulation. In thesimulation, clusters were “dynamically bridged” when the “bridge”devices alternated between the channels used by the different clusterson a frame-by-frame basis. As shown, clusters may be located relativelyclose to each other, or they can be more than 1 “hop” apart, i.e.,separated by more than one intermediary device.

It was found from the simulation that clustering of DSA-enabled devicesmay be capable of increasing the capacity of a DSA-enabled networkrelative to the capacity typically available in the absence of DSA, bysplitting the network into multiple channels. It was also found that thecoverage area of a DSA-enabled network may be increased by providing agateway to devices which cannot be accessed without routing traffic.Decisions within such a network may be made based on operator input. Asa specific example, in cell-tower scenarios a network may expandcapacity by splitting into clusters, each of which operates on adifferent channel or channels and includes a subset of the devices inthe network. In other cases, the DSA-enabled network may be joinedtogether by bridge devices which connect multi-channel clusters togetherand increase the coverage area.

In an embodiment, as larger bandwidth ranges are considered for use byDSA systems and, therefore, may be scanned by the DSA detectors, ahigh-level scheduler may be used to coordinate detection of signals.

The methods and systems for communicating coordination within a DSAnetwork as described herein may allow for various data to be sharedamong DSA-enabled devices in a DSA-enabled network. The informationshared among DSA-enabled devices may include relatively broad spectrumdata, such as measurements of energy in various channels observed by theDSA-enabled devices. Data relating to logical channel definitions may beshared, such as where a DSA-enabled device provides channelizationinformation to other DSA-enabled devices in the network. Data relatingto channel ranking also may be shared, such as where one or moreDSA-enabled devices shares a ranked list of channels preferred by thatDSA-enabled device with one or more other DSA-enabled devices in thenetwork. In an embodiment, some or all of the data shared among theDSA-enabled devices may be continually or periodically updated.

One potential impediment to successful operation of a DSA network may bethe successful detection of cooperative and/or non-cooperative spectrumusers, and the subsequent determination of whether spectrum is availablefor use by the DSA spectrum in a particular region. For example, if aDSA network has completely uncoordinated transmissions, detection ofnon-cooperative signals by DSA-enabled devices in a DSA-enabled networkmay be blocked by DSA transmissions. That is, a DSA-enabled deviceattempting to detect non-cooperative signals so as to avoid interferingwith them, may be unable to do so because those signals are masked orotherwise un-detectable due to transmission by cooperative DSA-enableddevices in the DSA network. For example, a detector may be blocked,desensitized, or otherwise affected by other DSA signals, or thedetector may incorrectly determine that spectrum is in use bynon-cooperative users.

It has been found that a signal classifier as described herein may beused to discriminate between DSA and non-cooperative signals andeliminate consideration of DSA signals as sources of non-cooperativespectrum use. In general, a signal classifier may detect andcharacterize each use of a spectrum bandlet, i.e., a region of spectrumwhich may be used for communication by a network, and estimate anychannelization of the bandlet. This may allow a DSA network to avoidcoordinating co-channel DSA communications to have specific, scheduled“off periods” to enable the system to “look through” its owntransmissions for non-cooperative users that may be coincident in time,frequency, and/or space with the DSA network. That is, in an embodimentof the present invention an efficient classifier may allow forcommunication among DSA-enabled devices without use of a synchronizeddetection gap as described herein.

It has also been found that the signal spectrum width and/or shape of asignal may provide a computationally-efficient way to differentiate DSAsignals from non-cooperative signals. That is, signals may be identifiedor classified based on the amount of bandwidth they occupy and/or theircorrelation to known signal masks. Such a method may be especiallycomputationally cost effective compared to examining other factors thatmay require additional processing, such as demodulating one or moresignals to examine the modulation type of each.

Referring again to FIGS. 1-2, a signal classifier 134 may analyze energydetected within one or more regions of the spectrum, such as outputprovided by the detector subsystem 112, and characterize channels inwhich a signal is detected according to the RF signature of the detectedsignal. The classifier may be configurable to classify signals asbelonging to one or more signal classifications from a predetermined setof signal classification types. Examples of predetermined signalclassification types, may include, for example, Control, Primary,Cleared, and Non-Cleared. These classification types also may bereferred to as channel states, since a DSA-enabled device or system mayassign each classification type to one or more channels based upon thesignal detected on the channel. Other classification types may be used,such as “Not Allowed” to represent portions of spectrum in which the DSAsystem is prohibited from operating, such as by policy constraints.Signals in regions of spectrum prohibited by policy constraints may notbe analyzed, or may be analyzed but labeled as Not Allowed. In general,virtually any type of signal classification type may be included in theset of signal classification types, and the list and description ofsignal classification types included herein is provided as an exampleand is not intended to limit the signal classification types. Theclassification of signals may be binary (i.e., each signal is or is nota particular signal type) or a classification type assigned to a channelmay be weighted by a confidence level.

The classifier 134 may be configured to periodically analyze channelsand classify the signals within the channels. Alternatively or inaddition, the classifier may be configured to analyze and classifysignals within a channel based on an event or command, where the eventor command need not be related to passage of time. For example, theclassifier may be triggered by arrival of detector outputs, regardlessof the frequency or specific time at which the output is provided.

The classifier may analyze channels within a region of spectrumconcurrently or may analyze channels in accordance with a schedule oralgorithm, such as described herein with respect to the scheduler 122.The classifier may analyze channels based on the information provided bythe various detectors and detector types included in the system. As aspecific example, detection results provided by a narrowband detectormay be used in an analysis of the counterpart channels in which thedetector is tuned. As another example, detection results provided by awideband detector may be used in analysis and classification of signalswithin a plurality of channels in a region of spectrum.

In some embodiments, the classifier may determine a classification typefor signals within a channel by applying one or more predeterminedsignal masks to detection results provided by the detector subsystem.For example, each classification type may have a counterpart signalmask. The classifier may then determine the classification type based onthe results from applying the various signal masks.

In some embodiments, the classifier may only or initially identify eachdetected signal only as cooperative or non-cooperative, without furtherclassifying the type or function of the signals. This may allow theDSA-enabled device or network to rapidly respond to the primary or onlyenvironments in which it should perform specific actions. For example, aDSA network may operate in a regular transmit/receive mode in which datais transmitted among DSA-enabled devices in the DSA network, until anon-cooperative signal is detected which indicates that a differentcommunication channel should be used. As another example, a DSA-enableddevice may operate in a detect-only mode until a DSA or cooperativesignal is identified, at which point the DSA-enabled device may attemptto join the associated DSA network. Thus, in many cases it may not benecessary for the classifier to classify detected signals or potentialsignals any further than indicating whether the signal is cooperative ornon-cooperative.

For example, the signal classifier may identify a signal that indicatesthe presence of a DSA-enabled device or network in a particular channel.Such a channel may be marked as a “Control” channel. Similarly, if anon-cooperative signal is detected then the channel may be marked“Primary.” As previously described, the classifier may notify aRendezvous subsystem if a primary signal is identified, which may causethe DSA-enabled device or network to initiate a channel switch. Channelsthat have neither cooperative nor non-cooperative signals may be markedas “Cleared.” A channel also may be marked as Cleared when a certainamount of time has elapsed without detecting a Control or Primary signalon a channel previously identified as a Control or Primary channel.Channels for which there is insufficient detector data to determine asignal classification above a predetermined false alarm rate also may bemarked as “Not-Cleared.” The specific definitions for variousclassification types used by the classifier may include additionalfeatures, and other classification types may be used.

According to an embodiment, example channel classification types may bedefined as shown below:

-   -   Not Allowed: A channel or region of spectrum that an active        policy restricts the DSA system from using.    -   Primary: A channel or region of spectrum in which a        non-cooperative signal has been detected. The non-cooperative        signals may be “primary” signals within a particular channel,        such as signals from a TV station operating in a region of        spectrum reserved for TV use in a regulatory framework. However,        the classification of a signal as Primary may not be limited to        identifying users or uses within a region of spectrum that are        “primary” within a specific regulatory framework. As a specific        example, the detection of a signal that may be considered a        secondary signal, such as a white space device operating in a        region of spectrum identified as reserved for TV use, may result        in a channel being marked as Primary since the secondary use        could cause interference to a DSA-enabled device operating        within that region of spectrum.    -   Control: A potential DSA channel. Multiple Control channels may        be identified.    -   Cleared: Neither cooperative nor non-cooperative signals have        been detected within a specified time span.    -   Not Cleared: An allowed channel that cannot be identified as        Primary, Control, or Cleared, such as channels outside the        bounds of the detector frequency range, and channels where        insufficient data has been collected to determine a valid state.

In some embodiments, more or fewer states may be used. For example, insome embodiments only two states (e.g., Cleared and Not Cleared) areused, which may be sufficient to avoid causing unwanted interferencewith non-cooperative users.

The classifier may update the state of each channel as defined by thechannel manager 132 periodically (e.g., every 100 milliseconds, 200 ms,500 ms, or any other suitable period), whenever one or more detectorscompletes a scan, or some combination thereof. Other triggering eventsmay cause the classifier to update the channel status, such as aninstruction defined by an enforced policy. As described with respect tothe detector subsystem 112, the detectors can be configured to scanperiodically, but need not necessarily scan synchronously with theupdates performed by the channel manager or the classifier, or wheninstructed by the communication coordinator 124 to go into a freewheel(constant detection) mode.

In some embodiments, the channels marked Control and Cleared define thelist of candidate channels that is utilized by the Rendezvous module. ACleared channel may be relevant to the rendezvous process as a channelthat can be used to establish a DSA network. Similarly, a Controlchannel may be relevant since it is a channel that may be usable to joina pre-existing DSA network.

According to embodiments of the invention, a signal classifier may beconfigured based on particular constraints or operational parametersimposed on the DSA-enabled devices within a system. For example, theclassifier may be different for DSA-enabled devices configured tooperate in bands originally licensed to TV broadcast as compared toDSA-enabled devices that are configured to operate in primarilyunlicensed bands. Several examples of signal classifier implementationsaccording to embodiments of the invention are described herein. However,the description and operation of each classifier described herein isprovided as an example, and does not operate to limit the scope oroperation of signal classifiers, in general.

According to an embodiment, a signal classifier may retrieve detectordata in the form of Fast Fourier Transfer (FFT) bin results. This typeof classifier may be referred to as a “Look-Through Version 1” (LT1)type classifier. Such a signal classifier may receive the FFT results asa plurality of bin magnitudes or as a plurality of complex values.

The LT1 signal classifier may receive detector output and divide thereceived data into a plurality of wideband channels. For example, thedetector output may be provided as a plot or list of detected signal orenergy levels at each frequency across the detector bandwidth. In aspecific example, an LT1 classifier may then divide this data into aplurality of, e.g., 2 MHz channels. Each channel may then be dividedinto a plurality of bins. For example, a 2 MHz channel may be dividedinto a plurality of bins each of which spans 25 kHz as shown in FIG. 25(not to scale, i.e., the correct number of bins is not shown). Otherdivisions are possible. In general, the precision of a signal maskincreases as more bins are used The signal classifier may then recordthe energy detected in each bin. The signal classifier may identify oneor more signals present by applying a predetermined signal mask to oneor more of the bins. In an embodiment, a channel may be identified ascontaining a DSA signal if the percentage of bins having a minimumenergy level exceeds a set level. This may correspond, for example, to aconfiguration where it is known or presumed that a DSA signal typicallyis wider than a non-cooperative signal expected in the region ofspectrum being analyzed. As a specific example, if at least 80% of thebins have at least −140 dBm/Hz, a channel including those bins may beindicated as having a DSA signal by the signal classifier. This value isonly illustrative and other values may be used depending on the noiselevel observed, which may vary with geography, altitude, and otherfactors as will be understood by one of skill in the art.

In some cases, an LT1-type signal classifier may not provide anacceptable probability of detection, or may generate too many falsealarms. In an embodiment of the invention, a Look-Through Version 2(LT2) signal classifier may be used to improve the probability ofdetection, decrease the number of false alarms, or both.

An example process suitable for use by a signal classifier according toembodiments of the invention which include an LT2-type signalclassifier, is shown in FIG. 26. At 6710 the signal classifier may firstexamine energy in the channel as measured by the detector subsystem todetermine if the channel contains a signal. The signal classifier maydetermine that a signal is present, for example, by comparing a signalenergy or signal magnitude in the channel to a predetermined threshold.The threshold may be determined, for example, based on the bandwidth ofthe channel, noise figure of the receiver, false alarm margin, and thelike, or combinations thereof. If no signal is detected, such as whereonly noise is detected in the channel, at 6715 the channel may beexcluded from further analysis and may be considered as a candidatechannel for use by the DSA network. For example, the channel may beclassified as a “cleared” channel as previously described. If a signalis detected, at 6720 the classifier may determine the type of signaldetected, such as wideband or narrowband. For example, upon determiningthat a signal has been detected, the signal classifier may examineportions of the channel for indications of narrowband signals.

Based on this determination, the classifier may assign a classificationto the channel accordingly. For example, in an embodiment in which DSAsignals are wideband signals, a channel in which a narrowband signal isdetected may be classified as unavailable for use by the DSA network.Such a channel may be identified as a “primary” channel or otherwiseindicated as a non-candidate channel at 6735. At 6740, if the channelhas not been eliminated from further analysis, the classifier maydetermine whether a detected signal is a cooperative signal or anon-cooperative signal of similar type (e.g., a wideband non-cooperativesignal detected by a wideband-type DSA network) As described in furtherdetail, this analysis may be performed by comparing the detected signalto a signal mask that defines the expected form of a cooperative signal.The classifier may then classify the channel accordingly at 6750, suchas by marking the channel as “primary” (for a same-type, non-cooperativesignal) or “control” (for a cooperative signal).

Other steps may be performed, and some steps may be repeated or omitted.As a specific example, in an embodiment the classifier may first searchfor a narrowband signal in one or more channels before excluding achannel containing a non-matching signal from further analysis. Such anembodiment is described in U.S. patent application Ser. No. 11/839,503,filed Aug. 15, 2007, entitled “Methods for Detecting and ClassifyingSignals Transmitted Over a Radio Frequency Spectrum,” the disclosure ofwhich is incorporated by reference herein in its entirety.

In general, an LT2-type signal classifier according to embodiments ofthe invention may divide detector output into one or more widebandchannels, as previously described with respect to LT1-type classifiers.The classifier may then compare the frequency plot of the signal in eachchannel to one or more signal masks of known cooperative signals. FIG.27 shows an example signal mask 2820 according to an embodiment of theinvention. A detected signal 2810 may be compared to the signal mask2820 to determine whether the signal is a cooperative or non-cooperativesignal. Other signal masks may be used. The signal classifier may storeone or more signal masks as, for example, a text file within adesignated portion of memory. The classifier may then access each signalmask as needed.

As illustrated by FIG. 27, signal masks used in embodiments of theinvention may be modeled as plots of measured power versus frequency,and a similar plot of data collected by the detector subsystem may becompared to the signal mask. By using the signal mask, the probabilityof false alarms caused by noise captured by the detector may be reducedin contrast to a configuration in which the percentage of spectrum binscontaining energy is used to classify a signal, such as in LT1-typeclassifiers as previously described. For example, in most cases it isunlikely that man-made noise will have the same spectrum shape as a DSAsignal represented by a particular signal mask, and such noise may beimmediately excluded from consideration as being a cooperative signal.Examples of such noise include man-made noise, spurious signals receivedby the detector, including internally-generated spurious signals(“detector spurs”), and other similar signals or potential signals.

In an embodiment, the classifier may store multiple signal masks, eachof which may correspond to a signal or signal type having a differentspectral distribution. The signal classifier may make numerous signalmask comparisons with the different signal mask types or may makenumerous comparisons with the same signal mask type, but over detectoroutputs from different spectrums. For example, the IEEE 802.16specification supports different channel bandwidths (e.g., 1.75, 3.5, 7and 10 MHz); a signal classifier configured to operate within such aregime may have a signal mask for each of these bandwidths.

After comparing the detector output in each channel to the signal mask,an LT2 signal classifier may compute a metric that reflects the degreeof correlation of the spectrum measurement to the signal mask. Based onthis metric, the signal classifier may indicate whether an observedsignal is a DSA signal or not. In some embodiments, the classifier mayassign a confidence score indicating the likelihood that the signal is aDSA signal. For example, a signal that perfectly matches the signal maskmay be given a 100% confidence score.

In an embodiment, a signal classifier may include a confidence modulefor determining the confidence score for each signal mask comparison.The formula for calculating the confidence score can depend on severalvariables, and may be adjustable by a user of the DSA-enabled device tofocus on specific scenarios and/or give more weight to certain aspectsof the signal mask. For example, an initial check may be performed toverify that a received signal is roughly similar in shape to a targetsignal mask. This may be done by comparing pass-bands and guard-bands(also referred to as “stop-bands”) of the signal and signal mask asshown in FIG. 28. In general, there can be several pass-bands andseveral stop-bands. A pass-band refers to a portion of spectrum of asignal between limiting frequencies that is transmitted with minimumrelative loss. A stop-band refers to a portion of spectrum of a signalbetween limiting frequencies that is transmitted with maximum relativeloss. The signal classifier may use the mean values over a band tosubstantially eliminate potential errors attributable to signals havinghigh peak-to-valley ratios. It is typically expected that the differencebetween the mean pass-band value and the mean stop-band values of thereceived signal will be roughly similar to that of the signal mask. Ifthis is not the case, then the “worst” or lowest possible score may beassigned and the received signal will be classified as a non-cooperativesignal. If the received signal passes the initial test, the scoringprocess may continue further by, for example, performing more detailedcomparisons with the signal mask. In an embodiment, only the pass-bandsare used in calculating the score, and the transition stop-bands are notused. Such a test may be used in situations in which there is too muchvariation in the shape of stop-bands between detector scans.

The signal classifier may use various metrics in assigning a confidencescore. In an embodiment, the following values may be calculated and usedfor each or all of the pass- and stop-bands:

D_mean—difference in “mean” values between the signal mask and thereceived signal in the bandD_var—difference in “variance” values between the signal mask and thereceived signal in the bandD_peak—peak-to-mean ratio of the received signal in the bandF_man—scaling factor for D_mean (may be user defined and read from aconfiguration file)F_var—scaling factor for D_var (may be user defined and read from aconfiguration file)F_peak—scaling factor for D_peak (may be user defined and read from aconfiguration file); in an embodiment if the signal is a low-powersignal (e.g., less than 15 dB above noise) then additional weight may beadded to D_peak because the shape of the signal becomes difficult todistinguish and the peak-to-mean ratio becomes crucial in avoiding falsealarms.Factor—Normalization factor for the band that is a function of the sizeof the band in relation to total signal mask size. For example, if astop-band is 10 frequency bins long and the total signal mask size is100 bins then the normalization factor for this band is 1/10.For each of the bands, the score may be calculated as:

Score_band=Factor*((F_mean*D_mean)+(F_var*D_var)+(F_peak*D_peak)).

As a specific example, for a perfect match of a detected signal to asignal mask, D_mean, D_var, and D_peak are equal to zero. Hence, thelower the score the higher correlation between the received signal andsignal mask.The total score of the received signal may be calculated as the sum ofscores of all pass- and stop-bands:

Score=Score_band_(—)1+Score_band_(—)2+Score_band_(—)3;

To convert this score into a value within 0-100 range (with 100 meaningperfect match with the signal mask) the following conversion may beperformed. For example, a MaxDSAScore value may be the maximum allowedscore in order for detected signal to be declared as a cooperativeDSA-enabled device, and any signals receiving a score higher than thiswill be marked as non-cooperative signals.For a maximum possible score MaxNcScore, if Score is greater thanMaxDSAScore then the received signal may be declared as anon-cooperative signal, and:

New_score=MIN(Score,MaxNcScore)−MaxDSAScore

Inverse_score=New_score/(MaxNcScore−MaxDSAScore)

Confidence_Score=100*Inverse_score.

If Score is less than MaxDSAScore then the received signal may bedeclared as cooperative and:

Inverse_Score=Score/MaxDSAScore;

Confidence_Score=(100−(100*Inverse_Score))

Where the resulting Confidence Score is a value between 0 and 100, with100 meaning the highest confidence in the decision.

Thus, the confidence score may take into account:

The difference in “mean” values between the signal mask and the receivedsignals in the two side guard-bands and center pass-band.

The difference in “variance” values between the signal mask and thereceived signals in the two side guard-bands and center pass-band.

The above values are being multiplied by user-defined constants in orderto increase the weight of a specific criteria (e.g., the difference invariance might be more “important” to a specific user than thedifference in mean values).

The difference between the amplitudes of the center pass-band and theside stop-bands. The peak-to-mean ratio of the signal mask versus thereceived signal.

As previously described, in general a higher correlation between thesignal mask and the received signal results in a higher assignedconfidence score.

Various other metrics may be used by a signal classifier according toembodiments of the invention, whether the classifier is an LT2-type oranother type of classifier. In general, any method suitable forcomparing the similarity of two curves may be used. As a specificexample, the classifier may eliminate from consideration any signalvalues not more than a certain amount above a set or determined noiselevel. For example, the classifier may consider only signal values morethan 5 dB above a determined noise level. Other cutoffs may be used. Theclassifier may then calculate the absolute difference between the signaland signal mask at each frequency point. The ranking of the signal maythen be defined as the sum of these absolute differences, normalized forthe number of values considered. This calculation may be done usinglogarithmic (dB) or linear power values. The use of linear power valuesmay give greater weight to the final ranking, whereas the use oflogarithmic (dB) values may cause relatively large signal values to becompressed and given relatively less weight than when linear powervalues are used. The specific values and calculations used may beselected based on, for example, the expected bandwidth of thecooperative or non-cooperative signals in a region, processingconstraints or preferences, or other criteria.

Signal masks and classification algorithms used in LT2-type embodimentsof the signal classifier may be implemented for OFDM signals, and may betailored to these signal's spectrum profiles. In an embodiment, theclassifier also may be configured to classify signals that are not OFDMtype signals. For example, in an embodiment, the classifier may classifyPSK and FSK signals. While the classification approach for other signaltypes involves generally the same classification process, therepresentation of suitable signal masks and associated algorithms usedto compute correlation metrics may be different than those describedabove.

A signal classifier according to another embodiment of the invention mayidentify and classify narrowband signals. For example, a narrowbandsignal classifier may analyze a relatively narrow region of the spectrum(e.g., 25 kHz) compared to the LT1- and LT2-type classifiers previouslydescribed. An example of a channel suitable for analysis by a narrowbandsignal classifier according to an embodiment of the invention is shownin FIG. 29. A narrowband signal classifier according to embodiments ofthe invention may be used in conjunction with, or independent of, theLT1 and/or LT2-type signal classifiers.

In an embodiment, a narrowband signal classifier may analyze a centralportion of a relatively narrow channel. For example, a signal classifiermay be configured to examine the signal in a central 25 kHz portion of a75 kHz channel. The classifier may indicate that there is a cooperativesignal present if the signal level in the central portion is above anenergy threshold observed in the “sidebands,” i.e., the portions oneither side of the central portion. In the specific example, theclassifier may indicate a cooperative signal if a signal of 30 dB ormore above the energy in the 25 kHz “sidebands” is observed. Otherlevels may be used.

Further examples of signal classifiers, specifically LT2-type signalclassifiers according to embodiments of the invention, are described ingreater detail in U.S. patent application Ser. No. 11/839,503, filedAug. 15, 2007, the disclosure of which is incorporated by referenceherein in its entirety.

In an embodiment, before beginning a classification process a signalclassifier may select a “target” (expected DSA) signal bandwidth that isdifferent than the bandwidth of non-cooperative signals expected to bepresent in the region of spectrum being analyzed. This may allow theclassifier to use a relatively simple FFT algorithm to distinguishbetween cooperative and non-cooperative signals since the classifier canperform accurate signal classification based entirely or substantiallyon the bandwidth and/or signal mask of the signals, instead ofdemodulating each received signal. Such an energy-based detector mayrequire fewer processing resources than other techniques, such asmodulation or packet shaping approaches.

In an embodiment, a DSA system may track the amount of noise observed ina region of spectrum over time and determine an expected minimum noisein the region. By taking this noise floor into account when classifyingdetected signals, the classifier may be more sensitive to signals. Forexample, it is expected that tracking the noise floor may result inabout a 5 dB gain in sensitivity relative to a comparable method thatdoes not track observed noise.

In an embodiment, the “scanning window” may be repositioned in time suchthat sequential windows overlap. That is, the classifier may initiallyanalyze a portion of detector data defined by the detector bandwidthBW_(D). The next portion of data scanned is selected to begin at aposition BW_(D)-BW_(C), where BW_(C) is the bandwidth of a cooperativesignal, instead of at a position shifted an amount equal to BW_(D).Similarly, a detector subsystem may use overlapping windows whenmeasuring energy in a region of spectrum. The use of overlappingscanning windows may allow for more efficient detection and/orclassification of signals, since it can prevent an observed signal frombeing “cut” by the arbitrary window boundary and, thus, misinterpretedby the classifier. It also may increase the likelihood of detecting andclassifying bursty signals. FIG. 30 shows a schematic illustration ofoverlapping scanning windows according to embodiments of the invention.For example, in FIG. 30 the initial scan may result in an incorrectclassification because only a part of the cooperative signal is includedin the scan. However, the cooperative signal is fully included in thesecond scan, thus allowing for a correct classification. In contrast, ifthe detector windows had no overlap, this would not be the case becauseonly the second portion of the cooperative signal would have beenincluded in the scan.

In some embodiments, various methods to analyze the shape of a detectedsignal may be used in addition to or instead of those previouslydescribed. For example, the classifier may first define a plurality offrequency bins for detector data as previously described. The classifiermay then determine the frequency bin having the peak amplitude andidentify the corresponding maximum amplitude, A_(max). The classifiermay define the edge of the signal to be a preset level, E, belowA_(max), and identify the largest and smallest frequencies having anamplitude equal to the signal edge A_(max)-E. The signal bandwidth maythen be defined to be the difference between the identified largest andsmallest frequencies. The level E may be, for example, 3 dB.

As another example, the signal classifier may generate a cumulativepower function from the power versus frequency plot by defining thevalue at each point of the function to be the sum of the power in acorresponding frequency bin and each lower or previous frequency bin.For example, the value at a first point of the cumulative function maybe defined as the power in the first frequency bin of the plot. Thevalue at a second point is defined as the sum of the power in the firstand second frequency bins, the value at a third point is the sum of thepower in the first, second, and third frequency bins, and so on, witheach point corresponding to a frequency bin of the data being analyzed.The cumulative power function may then be normalized for the last point,such that the cumulative power function ranges from at or near zero atthe first point to 1 at the last point. The signal bandwidth may bedefined to contain a certain portion, for example 90%, of the signalpower. Minimum and maximum frequencies may be defined in the region nearthe ends of the cumulative power function. For example, a minimumfrequency may be defined as the frequency where the normalizedcumulative power function is 0.05, and a maximum frequency where thenormalized function is 0.95. The signal bandwidth may then be defined asthe difference between the maximum and minimum frequencies.

In some embodiments, the signal classifier may use fixedchannelizations, i.e., the DSA or cooperative spectrum may start and endat known frequencies. In other embodiments, variable or random channelbandwidths may be used when analyzing detector data. Both fixed andvariable/random channels may or may not overlap in frequency. If thepotential channels overlap, additional processing resources may berequired to compare a potential signal to the signal mask since thereare substantially more possible frequency offset values than occur fornon-overlapping channels. However, the use of one or morechannelizations that include overlapping potential channels may allowfor more efficient spectrum use by a DSA system. For example, if thereis only 10 MHz of spectrum available for use by a DSA signal having achannel size of 2 MHz, using a fixed channelization that does not allowfor overlapping channels may allow for a single, relatively narrow(e.g., 25 kHz) non-cooperative signal to cause an entire 2 MHz ofspectrum to become unusable by the DSA system. In contrast, if the DSAsystem uses channels that overlap every 250 kHz, then thenon-cooperative signal may only cause 250 kHz of spectrum to becomeunusable, as all other channels will still be considered clear ofnon-cooperative use.

Data or instructions from other subsystems may be used to determine anappropriate channelization. For example, the signal classifier may useinformation from the logical channel table (LCT) as previously describedto optimize processing, such as information regarding expected bandwidthor spectrum locations of DSA signals. As a specific example, the LCT mayindicate that DSA channels are defined to start only on 1 MHz spectrumboundaries, in which case the classifier may apply a signal mask at 1MHz intervals, even where the logical channel unit (LCU) size is lessthan 1 MHz. This may significantly reduce processing requirements. Forexample, if the LCU size is 250 kHz but DSA channels start on 1 MHzboundaries, the processing load may be reduced by a factor of 4. Theclassifier also may obtain band-specific sensing requirements oranalysis constraints from the LCT. For example, the LCT may specifydifferent co-channel thresholds for different detectors used by the DSAsystem. Further details regarding the use of the LCT and LCUs have beenpreviously described herein.

In an embodiment, a signal also may be classified in the time domain. Insuch an embodiment, a detected signal may be compared to one or moretransmission lengths expected for a cooperative signal. If the signalmatches the appropriate signal mask and has a cooperative transmissionlength, the signal may be identified as a cooperative DSA signal. If thesignal matches the signal mask but does not have an expected cooperativetransmission length, it may be identified as a non-cooperative and/orprimary signal.

In an embodiment, multiple signal classifiers may be used, and may bematched to one or more detectors or detection techniques. For example, aDSA system may include a signal classifier for each signal type (radar,wireless microphone, etc.) the DSA system can detect.

The signal classifier may enter classification decisions into the LCT aspreviously described. Various other data also may be entered in the LCTor transmitted to other DSA subsystems. For example, the classifier mayenter confidence scores, quality metrics, or various combinationsthereof into the LCT. Examples of quality metrics include LCU peakpower, average power, and standard deviation around the average power.The channel quality metrics and confidence scores may be used by, forexample, the channel manager to distribute spectrum among the usetables.

In some embodiments, the signal classifier may have a restrictedoperation from that described, or may be omitted altogether. Forexample, all DSA systems or DSA-enabled devices in a geographic regionmay utilize a synchronized detection gap and standardized detectiontiming. Although such a configuration may allow for acceptable operationwithout the use of a signal classifier, it also may require precisetiming of the detection gap. A global synchronization scheme such as theGPS timing system may be used to achieve such synchronization. Asanother example, a dedicated control channel could be assigned toinstruct cooperative devices on how to locate other cooperative devices,or on which a broadcast beacon could be transmitted. As another example,separate classifiers may be used to identify non-cooperative signals andcooperative DSA signals.

In some embodiments, additional signal processing methods such asmodulation type determination may be applied by the signal classifier.Such methods may incur additional processing costs, but may provide moreaccurate signal classifications.

As previously described, a DSA-enabled device or network may use a rangeof frequencies and bandwidths. To provide control and assurance toregulators and stakeholders that the technology does not causeundesirable interference or have other adverse effects, policies may beimplemented on DSA-enabled devices to enforce adherence to regulatory orother requirements. Referring again to FIGS. 1-2, a policy module 140and related components may be used to implement and enforce thesepolicies in a DSA-enabled device.

As previously described, a DSA-enabled device may be described in termsof multiple modules or logical components, including a communicationstack and underlying radio hardware, detection hardware, the DSA system,and a policy module. The various components of a DSA system may interactwith the policy module 140 when determining spectrum accessopportunities that are currently available, e.g. frequencies, bandwidth,power level, or modulation techniques the device can use to transmitgiven its current environment. The DSA-enabled device or network mayexecute applicable strategies needed for transmissions to conform topolicies defined within and/or enforced by the policy module.

The policy module may cause the device to operate correctly and refrainfrom causing harmful interference by enforcing that a DSA-enabled deviceconfigures the radio to one of the approved states only and by filteringillegal transmission requests. For example manufacturer may implementcustom DSA devices, networks, or other systems. In an embodiment of theinvention, the policy module represents a standardized, accreditedmodule in order to conform to regulatory stakeholder requirements as thepolicy module represents the core “trusted” components on the radiodevice.

FIG. 31 shows a block diagram of a policy module according to anembodiment of the invention. The policy module may include a policymanager (PM) 4210, a database 4220, a policy conformance reasoner (PCR)4230 and a policy enforcer (PE) 4240. Depending on the resourcesavailable to the device, the Policy Module may be a part of aDSA-enabled device. Alternatively, the components of the policy modulemay be moved to a remote proxy and accessed remotely by the PolicyEnforcer on the radio.

The policy manager (PM) 4210 may act as a gateway to an accreditedpolicy module. The PM may process and respond to remote commands fromany authorized stakeholder and for maintaining a policy database. Thefollowing table lists an example of commands that may be supported bythe PM. Other commands and modes may be used.

Policy Add Adds a policy content to a persistent storage and associatesthe policy with a specific operational mode. The policy is activated ifit is part of a running mode. Delete Removes an association from aspecific operational mode. The policy is deactivated if part of arunning mode. The policy is removed if no more references exist. ModeAdd Creates a new blank mode. Delete Removes information about anon-running mode. Running mode cannot be deleted. Switch Stops currentlyrunning mode and starts the new mode. All policies associated with thenew mode are activated. All others are deactivated. Statistics StatusQuery Returns information on the current state of all policy components.Log Query Queries and returns information about device and policyactivities. Log Clears, prunes, or deletes specific entries from logs.ManipulationIn some embodiments, regulatory or service provider requirements mayspecify that the policy module use secure techniques to manage andenforce policies. As a specific example, the PM may use a X.509 PublicKey Infrastructure (PKI) or similar mechanism for authorization,authentication, and accounting of policies or policy requirements.

Example elements of policies according to embodiments of the inventionare provided in the table below. These examples are provided forillustration only, and policies used with embodiments of the inventionmay include additional or alternative elements. Different combinationsof policy elements may be used, and various elements may be used oromitted from a particular policy.

Spectrum Policy Descriptions Listen-Before-Talk based types LBT - Sameup and downlink frequencies LBT - Different, but known, up and downlinkfrequencies LBT - Different, but known, up and downlink frequencies,band plan known LBT - TV band (TV detector) Spatial Types Geographicborder field strength limits Database geographic/TV coverage area basedTemporal Types Beacon reception required to use band Time of Dayrestrictions Authorization for finite time duration (with periodicrenewals) Device Based Types Device Capability - Ability to measuresecond and third harmonic Device Capability - XG TX power spectrumdensity limit Adjustable C/N Limit for any policy (−6 dB (insignificantinterference impact to Primary users) and 20 dB (medium amount ofinterference impact to peer XG DSA-enabled devices)) Connectivity BasedTypes Beacon reception required to use band Connectivity requirement forany policy (can use certain bands only if connected to Spectrum Manager)Group based types Type 1 Group Behavior - Abandon channel if anyDSA-enabled device within certain range detects Non-cooperative signalType 2 Group Behavior - Determine XG TX power based on estimatedinterference probability (used Belief, Disbelief, and Ignoranceestimates fused with Dempster-Shafer Theory) DSA-enabled device Identifyrestrictions (e.g., use while airborne prohibited, use only in fixedapplications, Red Cross use only) Distributed control based typesAutomated policy updates if feedback indicates that existing policy isinsufficient for non-interference operations Automated policy updatesnotification of policy revocation or update by policy authorityThe PM may maintain a running mode and multiple standby modes. Each modemay be associated with a set of policies that should be enforced whenthe mode is activated. These may allow for pre-planned policyconfigurations that the DSA system can switch among as needed.

The policy enforcer (PE) 4240 may restrict access to a spectrum regionby a DSA-enabled device, by ensuring that the device's configurationconforms to regulatory and system policies. Filtering of transmissionrequests may be achieved by evaluating the current configuration of thedevice, current device component configurations, collected environmentaldata, and a specific transmission request against policy rules andconstraints. If there are no policy constraints that prohibit therequested transmission, the policy enforcer may allow the transmissionto take place; otherwise it may be prohibited. The PE may include acomponent which periodically compares channels considered for potentialuse by the DSA-enabled device against available policies. The PEmaintains representation of the current state of the device as well as acache of recent approvals and denials to allow for more rapid decisionsregarding channel use. For each channel, the PE maintains a set ofpre-approved device states that the DSA system must match in order to bepermitted to transmit. Each pre-approved state represents aconfiguration in terms of values and allowed deviation to parametersmaintained by the DSA system that are used for matching a request.Alternatively, for each channel the PE may inquire with the policyconformance reasoner (PCR) whether the current state for that channelwould be approved. The PE may maintain these decision caches, since PCRcalculations may be relatively computation-intensive. The PE may monitorchannels the DSA system is attempting to use and proactively enforcethat transmissions originating from the local device to satisfy policyrequirements.

In some embodiments the PCR may use policies expressed in a policylanguage. The language may be a declarative language for expressingpolicies and logic used for guiding operation of the devices. Exampleframeworks suitable for constructing the policy language include the WebOntology Language (OWL), and Semantic Web Rule Language (SWRL) availablefrom the World Wide Web Consortium (W3C).

Ontological concepts may be defined for expressing knowledge about aDSA-enabled device, its hardware and software components, protocolstacks, capabilities, and current state. Examples include an operationalconfiguration of a transmitter in terms of power and frequency, withhistorical data about collected signal detections from a detector. Byusing a structured language, the system may provide an interoperableframework for sharing and evaluating information across different radioimplementations. This may allow manufacturers to implement custom DSAsystem and stakeholders to certify and reuse the same policy module, ora base version of a policy module, on multiple platforms. The languagealso may allow stakeholders to express spectrum requirements using anabstract terminology without the need to understand specific radioimplementations, such as specific hardware configurations.

In an embodiment, the language defines concepts for expressingrestrictions on the devices and their states in terms of SWRL ruleconstraints. For example, rules may be defined for expressing theapplicability of a specific policy and for accordingly determiningactions the policy permits or prohibits a device to perform.

In an embodiment, the fundamental modeling primitive of the language isa policy (spectrum access control policy), which is associated with acollection of facts and constraints used to determine whether the policyapplies to the radio's current configuration. In general, two types ofpolicies may be used: (i) permissive policies that permit devices toaccess a spectrum whenever a device and its spectrum use data cansatisfy the policy's constraints; and (ii) prohibitive policies thatprohibit devices to access a spectrum whenever a device and its spectrumuse data violate one of the policy's constraints.

In an embodiment, the language may define terminology for allowing thearchitecture to operate in the presence of multiple policies frommultiple stakeholders. The policy module 140 may include functionalityto resolve conflicts among policies when multiple policies areactivated. In some embodiments a default de-confliction rule that aprohibitive policy overrides a permissive policy may be used. The rulemay be explicitly implemented by the policy module because the system'sprimary goal is to limit interference. A meta-level vocabulary fordefining absolute and relative prioritization of policies may be used tooverride the default rule. For example, the language may define avocabulary for assigning numeric priority levels to policies, and/or forrelatively ordering policies by defining relationships between pairs ofpolicies. The combination of a default rule and rule prioritizationschemata may determine an absolute order among policies, thus assuringenforcement consistence and correctness.

The PCR may evaluate policies, such as for syntax conformance andmeta-level validity, to confirm that the policy can be fully implementedand enforced by the policy module. Once validated, the PCR may convertthe policy into its internal representation, such as by extracting datadefined inside a policy document and loading the data into the policymodule internal database 4220. The PCR also may extract rules defined bythe policies and convert them into workflows to be used during operationof the DSA-enabled device. During the conversion process, the PCR mayoptimize the estimated execution time of each workflow by reorderingworkflow components based on an expected cardinality of answers andcomputing the complexity of each component. For example, the PCR maydefer all geospatial-computational workflow components, which typicallyare more computationally-intensive, to be processed afterknowledge-lookup components.

In an embodiment, the PCR may use a policy's meta-description to placethe policy in a list of active policies, which may be sorted byimportance or priority. Using this approach, the PCR may dynamicallymerge and de-conflict policies as they are made available to the radio.The de-confliction technique may apply the default rule for breakingties between permissive and prohibitive policies, and account fornumerical priority levels assigned to policies and relative policyordering. In such an embodiment, even in the event of one prohibitivepolicy and one permissive policy each being considered “more important”than each other (i.e. there is a cycle of importance among policies),application of a default rule may insure that a prohibitive policy takesprecedence and thus avoids potentially harmful interference by denying arequested transmission. This may reduce the workload required for thePCR to reach a transmission approval decision and to compute availablespectrum access opportunities.

In an embodiment, the policy module may prevent interference by a DSAsystem with non-cooperative networks by interrupting transmissioncommands sent to the radio. Before the radio transmits, the DSA systemmay first obtain an approval from the policy module. FIG. 32 shows anexample process for obtaining approval from a policy module according toan embodiment of the invention. In some embodiments, the policy modulemay have direct access to the hardware to preclude a DSA system fromsidestepping the policy module and transmitting using a disallowedconfiguration.

In an embodiment, the PE may maintain a set of pre-approved state modelsfor a DSA system based on configuration policies and an associated timeperiod during which the state is valid. The PE may assume that apre-approved device state would in fact be approved for some period oftime. This time period may be a time period as defined in, for example,the Dynamic Frequency Selection (DFS) standard.

In an embodiment, when no pre-approved state is applicable, the PE maygenerate and send a petition request to the PCR, which evaluates itagainst an ordered list of policies based on decreasing priority. ThePCR may use the first policy in the ordered list that applies to thepetition to approve or deny the proposed transmission.

Since policies may restrict spectrum access, a DSA system can use theconstraints to learn about newly-available channels and requirementsthat the DSA system should or must meet prior to transmitting on thosechannels. FIG. 33 which shows an example process according to anembodiment of the invention in which a DSA system obtains additionalinformation about spectrum availability based on policy information. Asshown, a DSA system may obtain the opportunities by submittingpartially-populated configuration states to the PCR. The PCT may thenevaluate the request against policies to identify missing values ofunpopulated parameters that would render the request a valid spectrumuse. As a specific example, the PCR may discover that for a submittedconfiguration to be approved, the transmission frequency must be either2310 MHz or 5180 MHz. In this case, the PCR returns two opportunities.

There may be situations when the PCR cannot find or fully populate anopportunity. If a request does not match any policy or if it violates apolicy, then no opportunity is found. On the other hand, a parameter maynot be bound if there is an unbound set of possible values. For example,while a value may be restricted to a certain range, depending on theaccuracy available to the system it may be verycomputationally-expensive to bind a device's position to be within thecontinental United States by enumerating all matching geospatialcoordinates.

As previously described, in general a policy manager 140 may interfacewith some or all of the other components of a DSA system, and may beinvolved in various processes performed during operation of aDSA-enabled device or network. In some embodiments, policy may beapplied more or less often to different channels or types of channels,and may be applied differently in different situations. For example,some tests have indicated that performing scanning and applying policiesto a relatively large number of channels may generate unacceptably highprocessing requirements. Therefore, some embodiments may apply policy toa subset of all possible channels, as previously described. For example,channels may be classified into several different types, and policiesmay be applied at different frequencies to each type, or not applied atall to some channel types.

In some cases, a DSA system may apply policy considerations to channelsother than those currently used by the system. For example, when aDSA-enabled device performs concurrent sensing and communication,policies may be applied to verify that channels identified as availableby a signal classifier are also allowed by one or more policiescurrently in effect. Checking policy (i.e., providing evidence to thepolicy module as previously described) at varying rates also maypreserve processing power. For example, the system may check policy witha relatively high frequency, and less frequently on other channels sincethere is no reason to check policy for an unused channel as frequentlyas the current channel if a signal has recently been detected in theother channel, since the other channel will not be considered availablefor use by the DSA system regardless. As a specific example, policy maybe checked for the current channel about ten times per second on thecurrent channel. The rate at which policy is checked or a channel may beset by regulatory requirements.

In some embodiments, the policy module may exert different influencesover the different channel use tables as previously described. Forexample, it may uses access control policies to determine what channelsare contained in the “possible” table. It also may influence thecontents of the other use tables by affecting the sensing and detectorrequirements which are used in the classification of channels. Therequirements may differ per channel. FIGS. 34A and B show examplelogical flows for applying policy requirements to use tables accordingto embodiments of the invention. As illustrated, the policy moduleperiodically may evaluate one or more use tables, such as the “possible”and “active” channel use tables. As previously described, the possibleuse table may be evaluated less frequently than the active table.

Periodically, every n period, the policy module may evaluate thepossible use table and the relevant spectrum access control policies tomake any changes to the possible table and any associated changes to therequirements for marking a channel as allowed for transmission. Thepolicy module also may evaluate the possible table whenever the spectrumaccess control policies are changed. Changes to the possible table andthe classification requirements may be made available to other DSAsystem components, and may indirectly influence other spectrum tables inconjunction with other system components as previously described.

Periodically, every m period, the policy module may evaluate the activeuse table and removes channels that are no longer allowed for useaccording to active policy requirements. The policy module also mayevaluate the active table when classification requirements change orwhen the channel manager or other system component attempts to add achannel into the active table.

In some embodiments, the policy module also may perform a policingfunction for other use tables, such as the active and backup use tables.That is, the policy manager may be able to “veto” or otherwise overridewhether a system can use a particular channel for transmission. FIG. 34Billustrates an example process on the active use table. The policymodule also may apply different rules and requirements to different usetables, such as where active spectrum is policed more vigorously, andbackup spectrum is actively, yet less frequently, policed. In someembodiments, the policy manager may not police some use categories atall. For example, possible spectrum often does not need to be policed.

The time periods described with respect to FIGS. 34A and B may vary, ormay be pre-set for different configurations. According to anillustrative embodiment, periods of 5 seconds and 60 seconds for the mand n periods, respectively, may be used.

The devices, systems, and methods described herein may haveapplicability to, and may provide various benefits to, a variety ofnetwork types and topologies. A few specific examples of applicationsand benefits of embodiments of the present invention will now bedescribed. It will be understood that these examples are provided by wayof illustration only, and other benefits and applications will beapparent to one of skill in the art.

The spectrum sensing and local adaptation functions described herein mayprovide information that is currently unavailable to conventionalnetworks, such as nearly continuous estimates of propagation lossbetween users, spectrum usage measurements with, for example, 10 to 20dB more sensitivity, and fewer “false positives.” This information mayimprove the performance of local resource allocation and may minimizestability problems because each DSA-enabled device will locally havemore and higher quality information to make determinations regardingspectrum usage.

DSA systems and methods also may provide benefits to existing,conventional network types such as, for example, wireless serviceproviders. For example, the use of DSA systems and methods may increasethe overall spectrum supply within a network, even where the network isgenerally restricted to a region of spectrum specified by regulatoryrequirements, by allowing for more efficient use of the spectrum. DSAsystems and methods also may increase utilization of encumberedspectrum, especially in the television bands, by allowing the relativelylarge portions of allocated but unused spectrum to be used by DSAnetworks without interfering with primary or co-primary uses ornetworks. For example, DSA may increase the utilization of the heavilyencumbered TV spectrum by using spatial and frequency holes in thespectrum (“white spaces”) and reducing or minimizing the risk ofinterference to primary users. Generally, DSA methods and systems alsomay reduce wireless system infrastructure costs, by enabling the use ofsignificantly more spectrum than is currently available to providers. Itis believed that shared spectrum usage as described herein may more thandouble the potentially-available spectrum.

DSA methods and systems also may enable spectrum trading and poolingwithin networks that would otherwise be limited to a set of fixed and/orpredefined regions of spectrum. For example, DSA systems enable spectrumtrading, leasing and pooling pursuant to the FCC's Secondary Marketsinitiative, which authorizes spectrum leasing by licensees to otherusers and networks. It is believed that there is a large amount ofspectrum that can be leased by many wireless services, including theCellular Radio Telephone Service, 700 MHz, Personal CommunicationsServices (PCS), Private Land Mobile Radio (PLMR), and Fixed MicrowaveServices. Licensees in these services are allowed to trade or leasetheir existing spectrum rights on a short- or long-term basis withminimal restrictions. Using DSA techniques, under-utilized spectrum maybe traded and accessed through private transactions, cooperatives, andthird-party band manager approaches. Spectrum license holders may havean incentive to lease spectrum to defray the high costs of spectrumpurchases from FCC auctions or as a revenue source. Spectrum-constrainedservice providers also may make temporary use of more favorably situatedspectrum. Other new users can lease spectrum for short-term high-valueitinerant applications. In a secondary spectrum market, DSA also mayovercome certain impediments to robust leasing including concerns that alessee's use could cause interference to the licensee. In some cases, itis believed that DSA may enable economical short time period leasing(minutes to months) instead of multiple-year leases.

DSA systems may lead to lower wireless infrastructure costs, includingbase station equipment. For example, the range of wireless links usingconventional technology is limited to short distances, typicallyhundreds of meters up to about 5 km, unless the DSA-enabled devices arewithin line-of-sight of each other. More transmitters and antennas arerequired in higher bands to overcome building and terrain obstructions.Erecting multiple towers, obtaining necessary zoning, variances, andlandlord permission is prohibitively expensive in most cases. DSA-basedwireless systems may allow for reuse of the lower bands in the UHF andVHF bands, where link range can exceed 15 km even in non-line-of-sightconditions, whereas systems in the higher microwave frequencies have arange of approximately 5 km in non-LOS conditions. The economic benefitsof this increased range may include a reduction in the number of basestations. The use of DSA also may reduce the number of new towers neededbecause it is believed that the existing radio tower infrastructure maybe sufficient for up to 100% coverage. Moreover, DSA may alloweconomical broadband Internet access to reach areas in which it waspreviously difficult or impossible to provide such access.

In general, embodiments described herein are relatively radio agnostic,i.e., may be used in conjunction with or implemented by any hardwareand/or software-defined radio. In some embodiments, upon power-up of theDSA-enabled device, a radio controller or radio interface module maycommunicates over a radio API to initialize modem hardware and configuretransmit/receive MAC data buffers for communication with the modemhardware. After initialization, the radio interface may await inboundpackets from the modem or transmits queued packets to the radio fortransmission over an assigned wireless channel.

Modem hardware may be implemented, for example, as an independentwireless transceiver, distinct transmitter and receiver modules, or oneor more wireless transceiver chips or chip sets. As an example, awireless transceiver may be based on a commercially available (COTS)802.16-based modem chip set.

In some embodiments, the data elements transferred to and from the radiomay include, for example, the frequency to be used by the radio totransmit and receive; a transmitter on/off signal; transmit/receive MACdata (output/input data queues); whether the radio state is synchronized(in a cooperative DSA network) or unsynchronized (in a free wheel mode)with respect to the detector; the type of radio (subscriber, basestation, etc.); whether the local oscillator is locked or unlocked; andwhether the power amplifier is on.

In an embodiment, modem capabilities may be stored in a predefined datastructure and may include information such as a frequency of operation(e.g. 225-600 MHz), maximum power, etc. The radio may contain a list offrequencies on which the radio is prevented from transmitting.

In an embodiment, a transceiver manager may interface with one or moretransceivers and operate to synchronize one or more detection gaps, forexample, among DSA-enabled devices. This transceiver manager may differfrom the scheduler 122 previously described by also schedulingintra-frame events. In some embodiments, the transceiver manager and thescheduler 122 may be a single module. For example, the scheduler 122 mayperform some or all of the functions described herein for thetransceiver module. The transceiver manager may also provide aninterface to and/or support for creating for a media access control(MAC) layer. In an embodiment, the transceiver manager interfaces to MACcomponents embodied in a transceiver chip. In another embodiment, thetransceiver manager provides the MAC components within the transceivermanager.

In an embodiment, the signal format of a DSA-enabled device may be basedon the IEEE 802.16 standard. The signal format is time divisionmultiplexed, and thus, has a time frame format. Each frame has aspecific sequence of events, which is described and implemented by thetransceiver manager. It will be understood that a DSA-enabled network orparticular DSA-enabled devices are not limited to any particularsignaling format, nor is a DSA-enabled device necessarily limited tosupporting only a single signaling format.

Two modes of operation may be implemented, RadioUDP and a VirtualNetwork Interface (VNIC) implementation. RadioUDP may be a simulatedradio interfacing to another type of network such as Ethernet. A VNICimplementation abstracts a real radio and may vary based on modem vendortype. An example VNIC mode using a COTS 802.16-based chipset accordingto embodiments of the invention will now be described; extensions andmodifications for use with a RadioUDP or other mode will be readilyapparent to one of skill in the art.

In such an embodiment, a frame may be initiated by a frame sync signalthat sets the start time of the frame. The 802.16 signal format isperformed in the COTS 802.16-based chipset/ASIC. The first segment ofthe frame is reserved for the base station (BS) burst, or uplink. ThisBS burst includes a preamble, network configuration data, and the MACdata. Before the start of a frame MAC data to be transmitted is queuedup for transmission, in the prior frame. At the tail end of the lastframe the local oscillator and RF/IF gain components are set. The localoscillator sets the radio center frequency, and requires a set up time,for example, up to 100 microseconds prior to reaching a stablefrequency.

After the frame sync, the ASIC initiates a transmission. It toggles thetransmit/receive of the radio to transmit. After a software programmedlead time, ASIC outputs digital data samples to, for example, IFhardware, such as an IF card. This lead time allows the RF circuitry tobe quiescent in the transmission state. The digital data samples startbeing converted to analog values within 10 microseconds. The ASICcontinues to stream out digital values which are converted to RF energywithin the RF/IF cards. At the end of the BS burst the transmit/receiveline is toggled to receive at a software controlled lag time after thelast digital data is flowed to the IF card. The lag time allows forlatency in this process and is set to, for example, 15 microseconds.This ends the BS burst time.

In parallel all subscribers are using synchronized framing events,within the downlink subframe. The subscriber during the first segment ofthe frame receives the BS burst. In the framing structure there is a gapin time between the BS burst and the first subscriber burst. During thisperiod the transceiver manager can be configured to instruct asubscriber to set the local oscillator and the RF/IF gain components.The local oscillator sets the radio center frequency. The RF/IF gainvalues are set by an automatic gain control module in firmware. Thereare generally three categories of gain: the preselector attenuation, theIF attenuation, and digital gain selection. The digital gain selectionis used to shift, for example, the bit position of a 10 bit sample valuewithin a 14 bit word analog sample value. This bit shifting is a lowlatency process since it can occur at the sample rate.

Following the BS burst the BS receives subscriber bursts in a sequence.This sequence is defined within a downlink map. The subscriber'stransmits data in a similar fashion as the BS but during their allottedtime slots within the downlink portion of the frame. Each subscribertime slot can be advanced to compensate for signal propagation delaysthat occur when the communication link range is expanded. The radiocomponent parameters are adjusted earlier than this advanced time.

The automatic gain control (AGC) feedback loop is used to set the properreceive attenuation. The subscriber measures the receiving signalstrength of the BS burst during its preamble time segment when the radiois time synchronized with the BS. If the signal strength is above thequiescent digital sample word value it increases the desired attenuationsetting by one step, if the signal strength is below the quiescentdigital sample word value it decreases the desired attenuation settingby one step. The link propagation loss may be assumed to be symmetricalsuch that the automatic level control (ALC) is tied to the AGCattenuation values. This ensures that the subscriber transmits a signallevel that will be properly received at the BS.

The subscriber firmware can be commanded by the DSA software to notexceed a certain power level, for interference mitigation reasons. Thiscommand clamps the maximum transmit section gain to not exceed a fixedvalue.

Following the BS burst and the subscriber bursts there is a reservedtime for one or more detection gaps as previously described. During thisperiod the transceiver manager instructs the local oscillator and theRF/IF gain components to be set. The local oscillator sets the radiocenter frequency. This center frequency may be different than thecommunication link frequency. The RF/IF gain components are set to keepthe signal environmental sensor within its dynamic range. Thepreselector is adjusted to maintain a low amount of intermodulationproducts. Once the local oscillator was sensed to have phase locked thedetector processing module is initiated. After this process completesthe sequence of events is at the beginning of the next frame. Thisrestarts the process of setting the proper components for the start ofthe frame just prior to the frame sync signal.

In an embodiment, the radio can be configured to use the same amplifierand attenuator circuitry for both transmission and reception. Since ingeneral the receive gain is not identical to the transmission gain thesettings for the gains change in within a frame.

In an embodiment, a data queue manager may ensure that control trafficfor a cooperative DSA network has low latency. The radio may have twodata flows—user data and cooperative DSA network control traffic. Toensure the radio switches rapidly during a rendezvous process, DSAcontrol traffic may be designated as higher priority traffic. Forexample, user (data) traffic may be placed in a common queue, and thecontrol traffic placed at the front of the queue. Thus, based onpacket/message type, the priority of a packet data unit in the queue maybe specified. This is an example of DSA QoS (Quality of Service)according to some embodiments, which may dramatically enhanceperformance of the DSA-enabled network.

As a DSA-enabled device and/or non-cooperative signal source move towardeach other, the system may need to switch quickly before an interferingsignal strength becomes so strong that it prohibits successfulcommunication. In some cases, the network will need to initiate a coldstart process, which may be more time consuming than performing channelswitching. In some cases, the transition between frequencies may resultin a temporary loss of connectivity, and/or a DSA-enabled device mayalso enter a “cold start” mode which may result in fairly significantloss of connectivity (100s of ms to seconds).

To minimize the effect of this behavior, a DSA-enabled device may alertthe underlying radio about impending transitions. In turn the radio mayprevent data packets from being transmitted, and buffer them untilconnectivity is reestablished. The radio driver also may prioritize DSAmanagement packets over all other traffic so as to speed up theconnectivity establishment/reestablishment process. An embodiment of thedriver architecture that supports queuing is illustrated in FIG. 35.

According to an embodiment, a dynamic transceiver control maydynamically adjust the transceiver RF and IF component settings(amplifier gain, pre-selector RF filter value, etc) to maximize receiversensitivity and maximize the shape of the transmitted spectrum. This mayreduce the need for high performance transceivers in co-site conditions,which significantly reduces radio costs. In some embodiments, whenstrong co-site signals cause frequency dependent distortion and signaloverload in the DSA-enabled device receiver, a DSA system may compensateby changing the operating frequency until a channel with minimaldistortion and overload is found. A dynamic transceiver control mayenable the DSA-enabled device to change both the transceiver settingsand change the operating frequency to find the best radio operatingpoint. By adapting both the transceiver settings and the operatingfrequency, the DSA-enabled device may obtain better receiversensitivity, which improves the link range or enables lower costhardware. Changing frequencies and changing transceiver settings toimprove receiver sensitivity use the same basic algorithm, hence,merging them together in a single process is the most efficientimplementation. Similarly, Dynamic Transceiver Control the DSAtransmitter settings, which may improve the transmitted waveform shape.

FIG. 36 shows an example DSA receiver RF circuit according to anembodiment of the invention. There are four component configurationparameters: (1) The Pre-selector is either tuned to the frequency ofinterest (in-band setting) or mis-tuned (Next Band) to provide a large(˜60 dB) loss. The amount of loss when the pre-selector is mis-tuned isfrequency dependent and usually not known. Additionally, thepre-selector has an additional signal path with a variable attenuator(RF ATT 2). This attenuator may have multiple settings e.g., 0 dB and 31dB. There is no filtering in this path. The purpose of RF ATT 2 is toenable operating in very high co-site conditions. (2) The RF ATTcontrols the amount of attenuation in the RF section. (3) The IF ATTcontrols the amount of attenuation in the IF section. (4) The ADC SHIFTcontrols the voltage range of the AD converter. It can be shifted up,for example, two bits.

In general, increasing the RF ATT, IF ATT or the ADC SHIFT valuesreduces distortion but increases thermal noise. Without co-site signalsand with weak DSA input signals, RF ATT, IF ATT or the ADC SHIFTsettings can be minimized to maximize sensitivity. With co-site signals,each of these parameters may be adjusted for optimal performance at acertain frequency. The RF signal path for the modem receiver and the DSADetector may be optimized with the same or similar hardwareconfiguration parameters since they share the same RF and IF hardware.

The table below shows example DSA Receiver hardware configurations.These configurations can be determined manually based on laboratorymeasurements of the hardware when in the same co-site conditions ofinterest. Different co-site conditions would have different hardwareconfiguration values.

Example DSA Receiver Hardware Configurations

Configuration Pre- RF ATT IF ATT ADC # Description Selector (dB) (dB)SHIFT 1 Max Loss Next 15 15 2 Band 2 Maximum In-Band 15 15 2 AttenuationSetting 3 Mid In-Band 10 10 1 Attenuation Setting 4 Low In-Band 5 5 0Attenuation Setting 5 No Attenuation In-Band 0 0 0 (Best NF) Setting

FIG. 37 shows an example DSA transmitter RF circuit according to anembodiment of the invention; specific examples of DSA transmitterhardware configurations are provided in the table below.Inter-modulation distortion may be caused by each amplifier in thetransmit circuit that tends to spread the transmitted spectrum, whichcauses unintended interference to non-cooperative transceivers. Bychanging the RF ATT and IF ATT values as a function of the operatingfrequency and the desired power levels, the transmitted spectrumspreading is minimized. These RF ATT and IF ATT may not depend on theco-site signal levels, but rather depend on the operating frequency, thesignal bandwidth, the modulation type and the transmit power level.

Example DSA Transmitter Hardware Configurations

Configuration RF ATT IF ATT # Description Pre-Selector (dB) (dB) 1Maximum TX In-Band Setting 0 0 Power Level 2 Medium TX In-Band Setting 55 Power Level 3 Medium TX In-Band Setting 10 10 Power Level 4 Minimum TXIn-Band Setting 15 15 Power Level

Co-Site Optimization Process Description

This section describes the algorithms used to optimize hardwareconfiguration settings to operate in the DSA system in the co-siteenvironment and the approach used to control these settings during the802.16 frame.

Sub-Band Frequency Plan

Because the co-site induced distortion effects and the co-site signalsare frequency dependent, the hardware configuration settings are varieddepending on the signal frequency of interest. The spectrum within eachpre-selector band is divided into sub-bands that are X MHz wide as shownin FIG. 37. The value of X is approximately equal to the transceiver IFfilter bandwidth. Typical values for X are 5 MHz and 10 MHz. TheDetector instantaneous bandwidth is equal or larger than the sub-bandwidth. If the Detector instantaneous bandwidth is less than the sub-bandwidth, then the Detector has to be called multiple times to measure thespectrum within the sub-band. This would be inefficient.

The table below shows in example hardware configuration table. InSub-band 3, there is a very strong co-site signal at 260 MHz. In thiscase, the RF ATT, IF ATT and ADC shift are the maximum values so thatthe signal is attenuated as much as possible.

Example DSA Receiver Configuration Table

DSA Receiver Setting Signal of Interest Pre- RF IF Sub- F1 F2 SelectorATT ATT ADC band (MHz) (MHz) Band (dB) (dB) SHIFT 1 225 235 1 4 0 0 2245 255 1 4 0 0 3 255 265 1 15 15 2 4 265 275 1 4 0 0 5 275 285 1 4 3 06 285 295 1 4 0 0 7 295 305 1 4 0 0 8 305 315 1 7 0 0 9 315 325 1 4 9 010 325 335 1 4 0 0 11 335 345 2 4 0 0 12 345 355 2 4 10 0 . . . . . . .. . . . . . . . . . . . . .

The DSA transmitter hardware settings may be determined to obtain adesired transmit power level, such as by calibration using a spectrumanalyzer. An output spectrum is measured for all RF and IF componentsettings and the measurements ordered by the transmit power level. Foreach output power level increment, the best spectrum is selected. Theassociated RF and IF component settings are then used as the tablevalues. In an operational mode, the hardware settings may be changedduring, for example, the 802.16 frame for the detector, the transmitter,and the receiver. Each of these operations may be performed at adifferent frequency. Periodically, during an operation mode, a test maybe made to determine if co-site conditions have changed and the abovecalibration needs to be repeated. A manual trigger may be used to makethis decision. Alternatively, an automated trigger may be used, whereone or more parameters may be used as the basis of the automatedtrigger. When triggered, the system will repeat the calibrationprocedure. All or part of the frequency list will be evaluated.

EXAMPLE HARDWARE FUNCTIONAL DESCRIPTION

This section describes the examples of hardware modules and componentsthat were built and used embodying at least portions of the DSAtechnology described herein. It will be understood that variouscombinations of hardware and/or software other than the specificexamples described herein may be used without departing from the scopeof the invention. For example, various hardware components may becombined, omitted, replaced, or otherwise altered from the followingexamples without changing the functionality or scope of the resultingsystem, as will be understood by one of skill in the art. Further, thevarious examples illustrate how DSA may be implemented on a variety ofradio types, although types other than those specifically described maybe used. Different MAC types (e.g., CSMA, TDMA and push-to-talk),detector types (e.g., FFT, cyclostationary, Ultra-Narrow bandwidth, andRSSI), and processors types (e.g., FPGA, DSP, GPP and limited capabilityprocessors) may be used. Different radio data rates also may be used.

An example DSA hardware system according to an embodiment of theinvention may include four circuit boards: (1) The RF Board, (2) the IFBoard, (3) the Digital Processing Board, and (4) the single boardcomputer. Several different RF boards may be used; several examples ofapplicable RF Board frequencies are provided in the table below.

RF Cards Suitable for Spectrum Bands Available to Different Classes ofUsers RF Board Public Safety RF Wireless (TV) Commercial RF #1 (MHz)Board (MHz) RF Board (MHz) Board (MHz) 225-512 138-174 174-216 698-9411215-1390 220-512 516-806 1390-1435 1435-1525 764-869 1670-26801755-1850 2200-2290

The RF Board's front-end has high filter selectivity and input interceptpoints, which is required for operation in an intentional interferenceenvironment. In contrast, most radios have poor selectivity and will notoperate well in a high signal level environment.

In the example embodiment, the IF board converts the IF signal at 1250MHz or 850 MHz (depending on the RF Board type) to 140 MHz, filters thesignal, and samples the 140 MHz signal. This digital data is sent to theDigital Processing Board. Other ranges and frequencies may be used.

The DPB may be, for example, a custom circuit board containing an FPGA,a DSP, and the 802.16-based modem ASIC as shown in FIG. 38. The boardmay be tailored to DSA requirements and is significantly different thanthe digital boards of conventional radios. It may support the DSP-basedDSA detection (on board), enables the use of an external DSA detector,and controls the transceiver.

FIG. 39 shows a schematic diagram of the various functions that may beimplemented by the DPB FPGA according to an embodiment of the invention.These functions may include, for example, digitally down-converting thedata signal using a mixer and low pass filter (LPF). An automatic gaincontrol (AGC) and an automatic level control (ALC) set the gain in theRF transceiver and the transmit power levels. Different AGC loops aremaintained for the modem and for the detector, which is required whenthe DSA transceivers are close together. The FPGA MAC function supportsthe 802.16-based chipset MAC function. The DSA detector reads data fromthe digital processor board memory, which is controlled by the FPGA.

The DPB uses a DSP to host the DSA detection algorithms. The DSP wasused to enable the DSA detection algorithms to be easily tailored to thespecific non-cooperative signal types. This DSP is a low cost (<$20),integer math engine with limited processing power so that commerciallyviable (low hardware cost) detection algorithms could be demonstrated.To meet both the performance and cost goals, the DSA detectorimplementations were designed around these fixed point and processinglimitations.

The DSP contains a variety of detectors that are selected based on thesignal of interest. The Wide Band Detector is an FFT-based detector thatwas optimized for execution speed and has limited dynamic range. It mostcases, in-band receiver high dynamic range is not needed since thespectrum measurements are usually made of empty spectrum or of very lowlevel signals. There is no requirement to measure high level signals.However, in most cases, there will be large out-of-band signals. Thisrequires high out-of-band receiver dynamic range. For example, in the TVband there is a combination of strong signals and empty spectrum. Inthis case, an associated detector may only need to measure the emptyspectrum accurately. When it measures the strong signals, it isirrelevant if there is distortion or other dynamic range problems sincethese channels will be judged used and unavailable. However, if thestrong signals are close in frequency to the empty channels, then theDSA receiver may require have sufficient dynamic range to reject theout-of-band strong signals when it measures the in-band empty spectrum.A similar situation occurs in co-site conditions near a cell phonetower. The DSA receiver may reject these strong cell phone base stationsignals when measuring spectrum in other bands. The PolyPhase FIR filteris a building block used by the Cyclostationary Detector and the TVdetector.

The IEEE 802.16 compliant modem is based on an ASIC made by athird-party COTS supplier. It is a high bit-rate modem intended to beused in static environments as a wireless local loop modem. Modulationis orthogonal frequency division multiplex (OFDM). OFDM sub-carriermodulation types include BPSK, QPSK, 16-QAM, and 64-QAM. The 802.16 airinterface protocol is intended to transport voice as well as data. TheIF bandwidth is variable, between 1.75 MHz and 10 MHz. The basebandinterface is Ethernet.

The time division multiple access (TDMA) frame structure is variableframe length of between 1 and 20 msec, with distinct uplink and downlinkburst time periods within each frame. Each frame has order wire slotswhich can be used by new network members to request time slots. Theframe is very flexible: Uplink and downlink burst time slots depend ontraffic loading. Users will be granted more time for their time slotsdepending upon the amount of data in their MAC queues (which depends ontraffic loading).

The General Purpose Processor (GPP) contains most of the DSA algorithmsand provides an external interface for control and data. The GPP may be,for example, an x86-based with a PCI, CompactPCI, or PC104/Plusinterface that operates with COTS operating systems.

Several different antenna types may be used. The example DSA-enableddevice has two antenna inputs, one for <1 GHz and another for >1 GHz.For omni-directional applications, wideband discones antennas are used.A discone antenna is used below 1 GHz. Another antenna type may be usedfor >1 GHz. In some applications, several types of Log Periodic antennas(LPA) may be used for <1 GHz.

It will be understood that the separation of functions described hereinmay be altered without departing from the scope of the inventiondescribed herein. For example, the signal classifier, channel ranker,and channel selector may be implemented as a single module. Variousmodules may be implemented entirely in hardware, such as in aspecial-purpose circuit, processor, or other device, or they may beimplemented in various hardware and/or software combinations as will beunderstood by one of skill in the art. The separation of functionalityinto specific modules described herein may be modified. For example, thefunctions performed by each module may be implemented in combinationsother than those specifically disclosed, and multiple functions may becombined into a single module even where they are described herein asperformed by separate modules.

In the foregoing description, for the purposes of illustration, methodswere described in a particular order. It should be appreciated that themethods may be performed in a different order than that described.Additionally, unless indicated otherwise the methods may containadditional steps or omit steps described herein. The methods may beperformed by hardware components or may be embodied in sequences ofmachine-executable instructions, which may be used to cause a machine,such as a general-purpose processor, special-purpose processor, or othercircuit or module to perform the methods. These machine-executableinstructions may be stored on one or more physical computer-readablestorage media, such as CD-ROMs or other type of optical disks, floppydiskettes, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, flashmemory, or other types of machine-readable mediums suitable for storingelectronic instructions. In some embodiments, a general-purposeprocessor or other physical device may operate in accordance with a setof machine-readable instructions to create or operate as aspecial-purpose device in accordance with the instructions. The methodsalso may be performed by a combination of hardware and software, whichmay be referred to as a module or circuit. Thus, as used herein, a“module” or “circuit” may include hardware, software, or any combinationthereof, as will be understood by one of skill in the art. Featuresdescribed in one embodiment may be used in other embodiments.

The disclosure of all references and publications cited above areexpressly incorporated by reference in their entireties to the sameextent as if each were incorporated by reference individually.

1. A method of classifying the status of a channel by a dynamic spectrumaccess-enabled device, said method comprising: determining achannelization for a region of spectrum; measuring energy present in aplurality of channels defined by the channelization; generating a firstconfidence score indicating the difference between a predefined signalmask and energy levels measured in a first group of the plurality ofchannels; generating a second confidence score indicating the differencebetween the predefined signal mask and energy levels measured in asecond group of the plurality of channels, the second group of channelsincluding at least one channel comprising a higher frequency than eachchannel in the first group of channels; and in response to at least oneof the first and second confidence scores exceeding a predefinedthreshold, classifying the corresponding group of channels as containinga cooperative signal.
 2. The method of claim 1, further comprisingclassifying the corresponding group of channels as containing a dynamicspectrum access signal.
 3. The method of claim 1, the first and secondgroup of channels having at least one channel in common.
 4. The methodof claim 1, the first and second group of channels having no channels incommon.
 5. The method of claim 1, wherein the frequency rangeencompassed by the first and second group of channels corresponds to apredefined channelization.
 6. The method of claim 1, wherein thechannelization is different than a channelization associated with anon-cooperative signal expected in the region of spectrum.
 7. A methodof operating a dynamic spectrum access-enabled device, said methodcomprising: determining a channelization for a region of spectrum;measuring energy present in at least one channel defined by thechannelization; based on the measured energy, identifying a signal inthe at least one channel; comparing the detected signal to a predefinedsignal mask, the signal mask defining a power-frequency relationship fora modeled signal in the at least one channel; calculating a confidencescore based on the comparison of the detected signal to the signal mask,the confidence score indicating the likelihood that the signal is acooperative signal; and based on the confidence score, classifying thesignal identified in the at least one channel as at least one of anon-cooperative signal, a primary signal, and a cooperative signal. 8.The method of claim 7, wherein the channelization is different than achannelization associated with a non-cooperative signal expected in theregion of spectrum.
 9. The method of claim 7, further comprising thestep of communicating with a cooperative device on the at least onechannel.
 10. The method of claim 7, further comprising: identifying aknown non-cooperative signal bandwidth corresponding to a region ofspectrum that includes the at least one channel; and selecting thesignal mask to have a bandwidth different than the non-cooperativesignal bandwidth.
 11. The method of claim 7, further comprising:identifying the type of signal detected in the at least one channel asbeing a type expected for a cooperative signal.
 12. The method of claim7, further comprising: prior to identifying the signal in the at leastone channel, measuring noise occurring in the channel for a period oftime; and reducing the value of the measured energy used to identify thesignal in said identifying step based on the noise measured during theperiod of time.
 13. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the difference in meanvalues between the signal mask and the detected signal in one or morepass-bands.
 14. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the difference in meanvalues between the signal mask and the detected signal in one or morestop-bands.
 15. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the difference in thevariance between the signal mask and the detected signal in one or morepass-bands.
 16. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the difference in thevariance between the signal mask and the detected signal in one or morestop-bands.
 17. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the distance betweenthe amplitude of the center pass-band of the detected signal and theside guard-bands of the detected signal; and calculating the differencebetween the calculated distance and the distance between the amplitudeof the center pass-band of the signal mask and the side guard-bands ofthe signal mask.
 18. The method of claim 7, said step of calculating theconfidence score further comprising: calculating the difference betweenthe peak-to-mean ratio of the signal mask and the peak-to-mean ratio ofthe detected signal.
 19. A dynamic spectrum access-enabled devicecomprising: a detector configured to measure energy present in at leastone channel; a first circuit to: identify a signal in the at least onechannel based on the energy measured by said detector; compare thedetected signal to a predefined signal mask, the signal mask defining apower-frequency relationship for a modeled signal in the at least onechannel; calculate a confidence score based on the comparison of thedetected signal to the signal mask, the confidence score indicating thelikelihood that the signal is a cooperative signal; and based on thecalculated confidence score, classify the signal identified in the atleast one channels as available for use by the device node.
 20. Thedevice of claim 19, wherein said first circuit comprises a signalclassifier.
 21. The device of claim 19, wherein said detector is furtherconfigured to measure energy present in at least one of a first sideportion and a second side portion of a narrow channel, the first sideportion being defined by a first frequency range and the second sideportion being defined a second frequency range, the second frequencyrange being higher than and non-overlapping with the first frequencyrange.
 22. The device of claim 21, further comprising a second circuitto define an energy threshold equal to the measured energy level; andmeasure energy present in a central portion of the narrow channel, thecentral portion being defined by a central frequency range between thefirst and second frequency ranges and, if the energy measured in thecentral portion is at least as great as the threshold, classify a signaldetected in the narrow channel as a cooperative signal.
 23. The deviceof claim 19, further comprising: a second circuit to determine theavailability of the at least one channel for use by the device based onsignal classification data received from the first circuit.
 24. Thedevice of claim 23, further comprising a policy module to specify howoften the detector measures energy in the at least one channel.
 25. Thedevice of claim 19, wherein said device is a secondary device in the atleast one channel.
 26. The device of claim 19, wherein said device is abase station.
 27. A method of identifying a cooperative signal by adynamic spectrum access-enabled device, said method comprising:measuring energy present in at least one of a first side portion and asecond side portion of a narrow channel, the first side portion beingdefined by a first frequency range and the second side portion beingdefined a second frequency range, the second frequency range beinghigher than and non-overlapping with the first frequency range; settingan energy threshold to be the value of the energy measured in said sideportion measuring step; measuring energy present in a central portion ofthe narrow channel, the central portion being defined by a centralfrequency range between the first and second frequency ranges; if theenergy measured in the central portion is at least as great as thethreshold, classifying a signal detected in the narrow channel as acooperative signal.
 28. The method of claim 27, wherein the narrowchannel is defined by a channelization different than a channelizationassociated with a non-cooperative signal expected in a region ofspectrum that includes the narrow channel.
 29. The method of claim 27,further comprising the step of communicating with a cooperative deviceon the narrow channel.
 30. The method of claim 27, further comprising:prior to classifying the signal as a cooperative signal, measuring noiseoccurring in the channel for a period of time; and reducing the value ofthe measured energy used to identify the signal in said classifying stepbased on the noise measured during the period of time.